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Appendix. Playbookof Bottleneck Solutions

Publication Number: FHWA-HRT-16-064 Date: November 2016

Publication Number: FHWA-HRT-16-064
Date: November 2016

Traffic Bottlenecks: Identification and Solutions

APPENDIX. PLAYBOOK OF BOTTLENECK SOLUTIONS

To solve the U.S. traffic congestion problem, mitigation or elimination of bottlenecks is believed to be a top priority. This report was intended to update the traditional approaches to congestion and provide new solutions. One of the modernized approaches is a comprehensive framework for congestion and bottleneck treatments developed for this report. The framework begins with a thorough definition of terminology and proceeds to a flowchart (playbook) of bottleneck classifications. The flowchart is shown in figure 29 in chapter 3. Within the 7 main classifications are 70 possible solutions, which are described further in this appendix.

(1) Geometric—Roadway Specific

Design Speed
1. Description/Definition of the Element:Design speed is a selected speed used to determine the various geometric design features of the roadway.⁽²⁾ Research confirms that lower speeds are safer and lowering speed limits can decrease both crash frequency and severity. There are two types of design speed as follows:
  1. Designated design speed: The speed established as part of the geometric design process for a specific segment of roadway.
  2. Inferred design speed: The maximum speed for which all critical design speed-related criteria are met at a particular location.
2. Theoretical/Empirical Effects:
  1. Speed-flow-density relationships are well established in the literature; speed is inversely related to density, which is used in the 2010 HCM as the measure of quality of traffic service for freeways and multilane highways.⁽⁶⁾ Speed and flow are related by a quadratic relationship, such that flow is maximized at an optimal speed above or below which flow decreases.^(63,88)
  2. Speed is used directly as a measure of mobility and facilities that emphasize mobility (highways/freeways) accommodate high speed.⁽⁶³⁾ As a result, lower speed causes lower flow, resulting in diminished capacity.
3. Existing Solutions:In general, speeds can be reduced/increased by changing the posted speed limit, geometric, and cross-sectional elements, or a combination of the following:
  1. Variable message signs.
  2. General VSLs (which may include volume, weather, or incident responsive).
  3. Increased lane and shoulder widths (which will impact operating speeds).
  4. Improved access management to decrease interchange or intersection density.
  5. Reduced excessive grades.
  6. Lengthening of vertical curve lengths.
  7. Increased horizontal curvature radius or increased superelevation where reasonable and safe.
4. New Solutions: New solutions include the following:
  1. Speed harmonization.
  2. More frequent VSL sign spacings.
  3. Speed limit specification by lane.
Number of Lanes

Description/Definition of the Element: Number of lanes is the available lanes in a particular direction for drivers to use.
Theoretical/Empirical Effects: The number of lanes is directly related to flow and determines the capacity of the roadway; however, if the lane is an auxiliary lane, the utilization may be low, thereby producing partial benefits.
Existing Solutions: Existing solutions include the following:
1. Plus lane (left/right).
2. Restripe narrower lanes to create new lane(s).
3. Build new lanes.
4. Managed lanes, including the following:
  1. Contraflow lanes.
  2. Reversible lanes.
  3. Bus-only or transit only lanes.
  4. High-occupancy toll (HOT)/HOV lanes.
5. HSR.
6. Dynamic lane control or moveable barrier separated lane control.
7. Shoulder conversion (i.e., permanent conversion of left and/or right shoulders to a travel lane).
New Solutions: New solutions include the following:
1. Electronic pavement marking on roadways.
2. Dynamic lane assignment for auxiliary lanes (i.e., convert option lanes between dedicated exit versus dedicated TH lanes based on DMS displays).

Lane Width

Description/Definition of the Element: This is defined as the width of driving lanes. The standard lane width on most roadways is 12 ft.
Theoretical/Empirical Effects: Narrow lanes reduce driver comfort, which cause drivers to slow down, reducing flow and capacity, particularly in locations with high volumes of oversize vehicles and large trucks. Other effects are as follows:
1. Narrow lane widths increase steering workload and reduce speeds.⁽⁸⁹⁾
2. Effective lane width reduction can reduce speeds by up to 7 percent.⁽⁹⁰⁾
3. Drivers implement direct control of lateral error for extreme conditions of narrow lane width and high speeds.⁽⁹¹⁾
4. Extra pavement contributes to the total amount of pavement width, which decreases drivers’ uncertainty and leads to higher speeds.⁽⁹²⁾
5. Lane width may increase the passenger car unit (capacity) of a roadway because of increased freedom of movement on wider roads.⁽⁹³⁾
Existing Solutions:Existing solutions include the following:
1. Widen lanes.
2. Auxiliary lanes.
3. Paved shoulder (right/left).
4. Heavy vehicle restriction.
New Solutions: New solutions include the following:
1. Static pavement marking changes: Change the lane width based on lane utilization on the road. For example, the rightmost lane dedicated to trucks could be wider than the middle lane(s) for passenger cars on the same road.
2. Electronic pavement marking on roadways: Create pavement markings on roadways.

Shoulder Width and Type
1. Description/Definition of the Element: It is the portion of the roadway contiguous with the traveled way for accommodation of stopped vehicles for emergency use and for lateral support of the base and surface courses.⁽⁹⁴⁾
2. Theoretical/Empirical Effects: Narrow shoulder widths might reduce driver comfort, causing drivers to reduce speeds, which results in reduced flow and capacity. Additional effects are as follows:
  1. As with pavement widths, the findings on shoulder width and crash rates are mixed. Similarly, some studies found no relationship between the right shoulder width and crash rates, while others have concluded that crash rates decreased as shoulder width increased.⁽⁹⁵⁾
  2. Extra pavement contributes to the total amount of pavement width which decreased drivers’ uncertainty and led to higher speeds.⁽⁹²⁾
3. Existing Solutions:Existing solutions include the following:
  1. Provide and/or upgrade shoulders.
  2. Widen shoulders.
  3. Paved shoulder (right/left).
  4. Auxiliary lanes using shoulder widths.
  5. HSR.
4. New Solutions: A new solution includes the following:
  1. Electronic pavement marking on roadways.
Lane Drops
1. Description/Definition of the Element:A dropped lane is a TH lane that becomes a mandatory turn lane on a conventional roadway or a TH lane that becomes a mandatory exit lane on a freeway or expressway. The end of an acceleration lane and reductions in the number of TH lanes that do not involve a mandatory turn or exit are not considered dropped lanes.⁽⁷⁹⁾
2. Theoretical/Empirical Effects:Inversely related to flow, a decrease in the number of TH lanes decreases the TH movement capacity on the roadway.
  1. Using data from a freeway lane drop in Minneapolis, it was shown that the discharge flow was about 10 percent lower than the prevailing flow observed prior to queue formation.⁽⁹⁶⁾
3. Existing Solutions: Existing solutions include the following:
  1. Advance lane drop warning.
  2. Late merge techniques.
  3. Dynamic merge techniques.
  4. Change/optimize the location of lane drops.
  5. Avoid lane drops at low-volume exit ramps.
  6. Run-by lanes.
4. New Solutions: A new solution includes the following:
  1. Dynamic lane use assignment using electronic pavement markings.
Lane Reduction Transition
1. Description/Definition of the Element: Lane reduction transitions are significantly different from lane drop situations because a lane reduction transition occurs between interchanges or between intersections. As a result, all vehicles in the ending lane must merge into the adjacent lane, while at a lane drop, vehicles that are unable to leave the lane have the ability to stay in the lane and proceed to the exit or turn.⁽⁷⁹⁾
2. Theoretical/Empirical Effects:Inversely related to flow, a decrease in the number of lanes decreases the capacity of the roadway.
3. Existing Solutions: Existing solutions include the following:
  1. Advance lane drop warning.
  2. Late merge techniques.
  3. Dynamic merge techniques.
  4. Change/optimize the location of lane drops.
4. New Solutions: None reported.
Horizontal Clearance
1. Description/Definition of the Element:Horizontal clearance is the lateral offset distance from the edge of the traveled way, shoulder, or other designated point to a vertical roadside element.⁽⁹⁷⁾
2. Theoretical/Empirical Effects: Reduced horizontal clearance may reduce driver comfort and cause drivers to reduce speed, which decreases flow and capacity.⁽⁹⁷⁾
3. Existing Solutions: Existing solutions include the following:
  1. Increase horizontal clearance.
  2. Remove any side blockage.
  3. Control roadway slopes to allow better vision.
  4. Create higher vertical clearances.
  5. Cut back on vegetation.
4. New Solutions: A new solution includes the following:
  1. Electronic pavement marking on roadways.
Vertical Clearance
1. Description/Definition of the Element:Vertical clearance is the maximum vertical height for a particular roadway and overpass clearance.
2. Theoretical/Empirical Effects:Even with sufficiently tall clearances, drivers may reduce speeds when light or moisture creates an optical illusion of a shorter clearance. The effect of vertical clearance is more pronounced for heavy vehicles.
3. Existing Solutions: Existing solutions include the following:
  1. Ensure placement of vertical clearance signs on structures.
  2. Mill pavement when necessary to avoid excessive layers of pavement over time when resurfacing.
  3. Ensure adequate design for overpasses.
4. New Solutions: A new solution includes the following:
  1. Vehicle height confirmation: Provide visual or audible confirmation through in-vehicle communication or roadside equipment that vehicle height does (or does not) exceed clearance.
Sun Glare
1. Description/Definition of the Element: Sun glare is the alignment of the road to environmental conditions including cardinal direction with respect to the possibility of sun glare.
2. Theoretical/Empirical Effects: Sun glare is shown to have a statistically significant impact on mean traffic speeds.⁽⁹⁸⁾
  1. Sunrise/sunset is listed as a distraction category in the Crashworthiness Data System and may contribute to crashes.⁽⁹⁹⁾
3. Existing Solutions: Existing solutions include the following:
  1. Roadway realignment.
  2. Backplates for traffic signals.
  3. Additional redundant TCDs.
4. New Solutions: New solutions include the following:
  1. Provide (visual or audible) confirmation of roadside conditions through in-vehicle communications or roadside equipment.
  2. Connected in-vehicle information on position of leading vehicles is not easily visible.
Horizontal Alignment
1. Description/Definition of the Element: In the design of highway alignment, it is necessary to establish the proper relation between design speed and curvature. The two basic elements of horizontal curves are curve radius and superelevation.⁽¹⁰⁰⁾
2. Theoretical/Empirical Effects: Curvature on the roadway causes reduced speeds and may limit stopping sight distance, which further reduces travel speeds.
  1. Deflection angle is the horizontal curve variable that best contributes to explaining the variation in speeds on a horizontal curve. High deflection angle values are associated with lower speeds.⁽¹⁰¹⁾
  2. Smaller curve radii result in poorer steering competence, which is compensated for by choosing a lower speed.⁽¹⁰²⁾
3. Existing Solutions: Existing solutions include the following:
  1. Increasing the horizontal curvature if it is applicable.
  2. Auxiliary/shoulder/plus lanes.
  3. Truck/heavy vehicle restrictions.
  4. Paved shoulder (right/left).
  5. Basic traffic signs and markings, enhanced/additional traffic control devices, rumble strips, minor roadway improvements, and innovative and experimental treatments.⁽¹⁰³⁾
  6. Static dual-advisory speed signing and pavement markings on freeway-to-freeway connectors.
  7. Sequential dynamic curve warning systems.⁽¹⁰⁴⁾
4. New Solutions: New solutions include the following:
  1. Dynamically triggered overhead or roadside mounted signs encouraging drivers to maintain posted or advisory speeds on curved sections when free flow traffic conditions prevail.
  2. Connected in-vehicle information on position of leading vehicles not easily visible.
Vertical Alignment/Grades
1. Description/Definition of the Element: Vertical curves are used to transition from one grade (i.e., slope in the direction of travel) to another.⁽⁸⁸⁾ It also refers to the grading angles on the roadway.
2. Theoretical/Empirical Effects: Increased gravity causes speed reductions on uphill grades and speed increases on downhill grades. On downhill sections, drivers may brake to compensate. In general, heavy vehicles travel slower on uphill grades than on downhill grades due to the physical characteristics of those vehicles (e.g., power of engine, weight, braking ability, etc.).
  1. Vertical alignment affects both driver comfort and sight distance. Crest vertical curves can limit sight distance by restricting a driver’s line of sight, but where vertical curves are long enough to provide adequate sight distance, they will also provide adequate driver comfort.⁽⁸⁸⁾
3. Existing Solutions: Existing solutions include the following:
  1. Reducing steep grades.
  2. Warning signs and flashing lights.
  3. Careful placement of TCDs around steep vertical grades.
4. New Solutions: New solutions include the following:
  1. Dynamically triggered overhead or roadside-mounted signs encouraging drivers to maintain posted or advisory speeds on grades when free-flow traffic conditions prevail.
  2. Connected in-vehicle information on position of leading vehicles not easily visible.
Stopping Sight Distance
1. Description/Definition of the Element:Stopping sight distance is defined as the distance needed for drivers to see an object on the roadway ahead and bring their vehicles to a safe stop before colliding with the object.⁽¹⁰⁵⁾
2. Theoretical/Empirical Effects:Insufficient stopping sight may cause sudden vehicles brake, shock waves, and/or collision. Physical barriers, roadway alignments, curves, time of day, and other factors affect the stopping sight distance.⁽¹⁰⁵⁾
3. Existing Solutions: Existing solutions include the following:
  1. Improve stopping sight distance.
  2. Reduce speed limits.
  3. ITS—queue warning.
  4. Reduce steep grades.
  5. Create higher vertical clearances.
  6. Cut back on vegetation.
4. New Solutions: A new solution includes the following:
  1. ATM solutions.

Pavement Friction
1. Description/Definition of the Element:Pavement friction is determined by the roughness level of the roadway surface pavement.
2. Theoretical/Empirical Effects:Lower pavement friction (e.g., when pavement is wet) may cause driver discomfort that results in speed reduction.
  1. Higher pavement friction results in fewer crashes stemming from wet pavement.⁽¹⁰⁶⁾
  2. Drivers on a curve experience unbalanced lateral acceleration (i.e., side friction), which is a direct indication of driver discomfort. Observed speeds on horizontal curves routinely exceed designated design speeds. The maximum friction factors used for the design speeds are intended to be adequate even under poor conditions; therefore, in average conditions, higher speeds can be attained. Steeper curves require a higher friction factor, which lowers the design speed.⁽⁸⁸⁾
3. Existing Solutions: Existing solutions include the following:
  1. Warning signs.
  2. Reduce speed limit.
  3. Reducing excessive grades.
  4. Weather responsive speed limits.
  5. Pavement techniques that increase friction include grooved, textured, or open-graded pavement. Grooving longitudinally reduces the noise while driving.⁽¹⁰⁵⁾
4. New Solutions: A new solution includes the following:
  1. Installing dynamically triggered overhead or roadside-mounted signs encourages drivers to maintain posted or advisory speeds based on pavement condition.

Cross Slope
1. Description/Definition of the Element:The cross section slope (perpendicular plane to the flow of vehicles) mainly assists in rainfall drainage.
2. Theoretical/Empirical Effects:Improper cross slope may cause speed reductions during inclement weather conditions because of insufficient drainage.
3. Existing Solutions: Existing solutions include the following:
  1. Maintain a cross slope along the roadway.
  2. Add more pipes for water storm drainage.
  3. Adjustment of the high-side shoulder cross slope to avoid melting snow and ice draining into roadway.⁽¹⁰⁵⁾
4. New Solutions: A new solution includes the following:
  1. Installing dynamically triggered overhead or roadside-mounted signs encourages drivers to maintain posted or advisory speeds based on pavement condition.

Superelevation
1. Description/Definition of the Element Superelevation is the rotation of the pavement on the approach to and through a horizontal curve. Superelevation is intended to assist the driver by counteracting the lateral acceleration produced by tracking the curve. It is expressed as a decimal, representing the ratio of the pavement slope to width and ranging from 0 to 0.12 ft/ft. The adopted criteria allow for the use of maximum superelevation rates from 0.04 to 0.12. Maximum superelevation rates for design are established by policy by each State.⁽¹⁰⁵⁾
2. Theoretical/Empirical Effects: Insufficient superelevation requires vehicles to slow down, and excessive superelevation may reduce driver comfort. In addition, some curves are not provided with superelevation, which leads to severe reduction of speed to prevent crashes or getting off the road.
  1. Superelevation allows a driver to negotiate a curve at a higher speed than would otherwise be comfortable.⁽¹⁰⁷⁾
3. Existing Solutions: Existing solutions include the following:
  1. Reduce speed limit for poorly designed superelevation.
  2. Design superelevation specifically for the site.⁽¹⁰⁷⁾
  3. Appropriate signage for drivers.
4. New Solutions: A new solution includes the following:
  1. Installing dynamically triggered overhead or roadside-mounted signs encourages drivers to maintain posted or advisory speeds based on pavement condition.

Access Density
1. Description/Definition of the Element: Access density is the number of access points and driveways per unit distance.⁽¹⁰⁸⁾
  1. Access point: An access point is an entrance, driveway, street, private drive, turnout, or other means of providing for the movement of vehicles to or from the public roadway network.⁽¹⁰⁹⁾
  2. Driveway: A driveway serves a single use on one property or multiple uses on more than one property.⁽¹⁰⁹⁾
2. Theoretical/Empirical Effects: Traffic friction from entering/exiting vehicles creates turbulence in the traffic flow.
  1. Speeds decrease as the number of access points increases.^(101,108)
3. Existing Solutions: Existing solutions include the following:
  1. Better access management, fewer access points, access point consolidation, better access point placement, better roadway signing, etc.
  2. Access roads, feeder roads, and limited access roads.
  3. Signals and other traffic control devices.
  4. Alternative intersection designs should be considered at key access points.
4. New Solutions: A new solution includes the following:
  1. Dynamic ramp metering at access points.

Midblock Pedestrian Crossings
1. Description/Definition of the Element:A midblock pedestrian crossing is a pedestrian crossing at designated pedestrian crosswalks.
2. Theoretical/Empirical Effects: Lower speeds occur as pedestrian activity increases.
3. Existing Solutions: Existing solutions include the following:
  1. Marked crosswalks for better driver yielding compliance, including use of rectangular rapid flashing beacons.
  2. Walk symbols that give enough time to cross.
  3. Enforcement.
  4. More meaningful positioning (e.g., crosswalks where people want to cross naturally) of midblock crosswalks in high-traffic areas.
  5. Bulbs, chokers, and neck downs, which all extend the sidewalk into the street to slow traffic and guide pedestrians.⁽¹¹⁰⁾
4. New Solutions: None reported.

Medians
1. Description/Definition of the Element: Medians constitute a portion of a highway separating opposing directions of the traveled way.^(63,111)
2. Theoretical/Empirical Effects:
  1. The presence of a median contributes to higher speeds than when no median is present.⁽¹⁰¹⁾
  2. When present, a raised, depressed, or two-way LT lane median results in slightly lower speeds.⁽¹⁰⁸⁾
  3. Medians can be designed to increase speeds, lower speeds using traffic calming islands or medians, or separate high-speed roadways.
3. Existing Solutions: Existing solutions include the following:
  1. Use for separation.
  2. Use for traffic calming.
  3. Use for pedestrian refuges.
  4. The presence of trees slows drivers as well.⁽⁶⁵⁾
4. New Solutions: None reported.

Lighting
1. Description/Definition of the Element:It is necessary to have sufficient roadway lighting for driving during dark conditions.
2. Theoretical/Empirical Effects: Insufficient lighting may cause drivers to reduce speed and use extra caution, reducing flow and capacity. Drivers may also misread or fail to observe a TCD indication causing incidents. Lighting generally improves sight distance and results in better safety performance.
3. Existing Solutions: Existing solutions include the following:
  1. Improve lighting and reflectivity of roadway signs and pavement markings.
  2. Provide (visual/audible) confirmation through in-vehicle equipment to inform driver of roadside conditions.
4. New Solutions: A new solution includes the following:
  1. Installing dynamically triggered overhead or roadside mounted signs encourages drivers to maintain posted or advisory speeds based on lighting conditions.

Presence of a Centerline or Edgeline Markings
1. Description/Definition of the Element: Centerline and edgeline road markings indicate traffic lanes, oncoming traffic, passing rules, and other traffic laws.
2. Theoretical/Empirical Effects:
  1. Absence of centerline or edgeline markings is associated with lower speeds.⁽¹⁰⁸⁾ Likewise, the presence of edgelines and centerlines is associated with higher travel speeds.⁽¹¹²⁾
  2. Road lines may not be visible in rain and snowy conditions.
  3. Centerline and edgelines guide drivers and reduce congestion and raise roadway capacity.⁽¹¹²⁾
  4. Lane markings reduce crashes.⁽¹¹²⁾
3. Existing Solutions: Existing solutions include the following:
  1. Uniform colors and meanings for better driver compliance.
  2. Durability with high-quality paint.
  3. Adding edgelines to rural roads.
  4. Better reflectivity and frequent reflectivity assessment (because pavement markings are most effective when there is poor visibility).⁽¹¹²⁾
4. New Solutions: A new solution includes the following:
  1. Electronic pavement marking on roadways.

Bicycle Lanes
1. Description/Definition of the Element: A restricted right-of-way that utilizes city streets, secondary roads, and other existing facilities and is appropriately designated by signs, lane markings, and/or physical barriers, such as guardrails, special fencing, curbed, or parked vehicles.⁽¹¹³⁾
2. Theoretical/Empirical Effects: Drivers may reduce speed around bicycles when there is no bike lane but, if provided with adequate width, may not need to adjust speeds.
  1. Bicycle lanes, when placed on streets without parking and of adequate width, appear to have little detrimental effect on traffic flow and may serve the beneficial purpose of providing better separation between vehicles and bicycles.⁽¹¹³⁾
  2. The presence of bicycles negatively affects auto flow (in terms of speed reduction and lateral movement) by limiting the usable roadway width. These negative impacts seem to be reduced or removed if a bike lane or a wide enough curve lane is provided.⁽¹¹⁴⁾
3. Existing Solutions: Existing solutions include the following:
  1. Widen or restripe lanes, create median refuges at street crossings, add bike-friendly signals, provide new bike trails in new communities where possible, and/or install bike-sensitive detectors.⁽¹¹⁵⁾
  2. Shared lanes, wide outside lanes, bike lanes, shoulder, and separate bike path.⁽¹¹⁶⁾
4. New Solutions: A new solution includes the following:
  1. Electronic Pavement Marking on Roadways to dynamically include bike lanes and dynamically change the width and/or separation of bike lanes to make them safer.

Separation Type of Managed Lanes
1. Description/Definition of the Element:Separation lines include a set of lanes with access restrictions (e.g., vehicle occupancy or tolled) located within a freeway but separated from the general purpose lanes.
2. Theoretical/Empirical Effects:By separating traffic between the managed and general purpose lanes, users in the managed lanes will experience an increased LOS over the general purpose lanes while at the same time, the decrease in demand for the general purpose lanes will increase the LOS for the general purpose lanes.
3. Existing Solutions:Existing solutions include the following:
  1. Managed access points.
  2. Movable separation barriers.
  3. ITS monitoring.
  4. Electronic toll collection (if appropriate).
4. New Solutions: None reported.

(2) Geometric—Facility Specific

Bridges
1. Description/Definition of the Element: A structure carrying a roadway over waterways or other surface feature including other roads, railroads, or other obstacles.
2. Theoretical/Empirical Effects: Drivers may reduce speed to use extra caution or use overload bypass routes. The effect may be more pronounced for heavy vehicles.
  1. Performance changes near temporary bridges demonstrate the effect of bridges on traffic flows. Lower speeds and higher average headways limit volume and throughput at the bridge.⁽¹¹⁷⁾
  2. A narrowed cross section (of a bridge) can make some drivers uncomfortable and cause them to dramatically reduce speed, degrading operations on high-speed, high-volume facilities, inadequate space for storage of disabled vehicles, enforcement activities, emergency response, or maintenance work.⁽¹⁰⁵⁾
3. Existing Solutions: Existing solutions include the following:
  1. Restriping to decrease lane width and add lanes.⁽¹¹⁸⁾
  2. Widening lanes.
  3. Truck restrictions.
  4. Traffic diversion.
  5. Build shoulders or medians on bridges for stopped and disabled vehicles and accidents.⁽¹¹⁹⁾
  6. Use ITS to alert drivers to bridge openings and/or sudden stops.⁽¹¹⁹⁾
  7. Reduce grades at bridge entrances to increase sightlines.⁽¹¹⁹⁾
  8. Discourage lane changing using pavement markings.
  9. Contraflow lanes—use of moveable barrier systems to change cross section by time of day.
  10. Reversible lanes.⁽¹²⁰⁾
  11. Congestion pricing to manage demand.
4. New Solutions: New solutions include the following:
  1. Installing dynamically triggered overhead or roadside mounted signs encourages drivers to maintain posted or advisory speeds based on lighting conditions.
  2. DRLT lanes.⁽⁸²⁾

Tunnels and Underpasses
1. Description/Definition of the Element: A tunnel is a roadway that traverses waterways or other bodies by going underneath. An underpass is the roadway that goes under a bridge or other structure.
2. Theoretical/Empirical Effects:Drivers may reduce speed or use overload bypass routes. Even sufficiently tall clearances may reduce speeds when light or moisture creates an optical illusion of a shorter clearance and the effect of vertical clearance is more pronounced for heavy vehicles.
  1. Congested flow at most sections of a tunnel has relatively little to do with the tunnel environment but rather is a consequence of bottlenecking or queuing processes because vehicle passing, merging, and diverging are less common in tunnels. Tunnel flow is one of the least complex of all flow situations.⁽¹²¹⁾
  2. When lane widths decrease on surface roads, traffic slows. Traffic also slows when ceiling heights decrease.⁽¹²²⁾
  3. Obstacles that are close to travel lanes (bridge abutments, piers, sign structures) cause driver slowing due the shy distance.
3. Existing Solutions: Existing solutions include the following:
  1. Adequate lighting.
  2. Adequate lane widths.
  3. Signage indicating actual height above each lane to allow drivers of tall vehicles to select the appropriate lane. Include advance signage to warn drivers to move to high-clearance lane. Knowledge of actual clearance gives driver confidence and avoids panic breaking.
  4. Restrict lane change and passing.
  5. Add lane using vertical bridge abutments (e.g., add lane between bridge pier and abutment replacing slope paving).
  6. Higher ceilings.
  7. Congestion pricing to manage demand.
  8. Move tolls booths away from entrances or exits.
4. New Solutions: A new solution includes the following:
  1. Mainline metering similar to freeway-to-freeway metering (i.e., ramp metering technology applied to the main area of roadways).⁽¹²³⁾

Collector-Distributor Network
1. Description/Definition of the Element:A collector-distributor network is a network of roads that efficiently distributes cars from smaller roads that have access to residential neighborhoods to larger roads with limited access points. This network consists of low to moderate capacity roads that serve to move traffic from local streets to arterial roads. In some States, such as Texas, collector-distributor roadways are a supplemental facility between freeway main lanes andthe frontage roads. Their primary purpose is to move the weaving and lane changing away from the high-speed traffic on the freeway main lanes.⁽¹²⁴⁾
2. Theoretical/Empirical Effects:Entering/exiting vehicles to/from the collector-distributor create friction, which causes speed reduction. Collector-distributor facilities can allow a single freeway exit ramp to distribute vehicles to two or more crossing arterials or collect vehicles from several crossing arterials so that they can enter the freeway at a single entrance ramp.
3. Existing Solutions: Existing solutions include the following:
  1. Limits to local traffic only.
  2. Limiting access.
4. New Solutions: None reported.

(3) Geometric—Specific to Interchanges: Freeway to Freeway

Diverge Sections and Merge Sections
1. Description/Definition of the Element: Diverge and merge sections consist of areas for exiting highways (e.g., off-ramps and areas for entering highways, on-ramps, and where highways join or split).⁽⁶⁾
2. Theoretical/Empirical Effects: Merging and diverging segments create confusion and chaotic movements often resulting from swift lane changing.⁽⁶⁾
3. Existing Solutions: Existing solutions include the following:
  1. Ramp metering.
  2. Swift lane changing.
  3. Appropriate signage.
  4. Appropriate Interchange spacing.
  5. Ramp modification—reversal (i.e., switching entrance and exit ramp pattern).
  6. Ramp modification—closure (i.e., permanent versus time of day).
  7. Option lanes.
  8. Proper lane balance and basic lanes (may be able to reduce number of basic lanes on TH roadways to allow more lanes for merging traffic from high-volume direct connect ramps).
4. New Solutions: New solutions include the following:
  1. Mainline metering.⁽¹²³⁾
  2. DMC (or junction control) to regulate or close specific lanes upstream of an interchange.⁽¹²⁵⁾

Auxiliary Lanes
1. Description/Definition of the Element:
  1. An auxiliary lane is defined by AASHTO as the portion of the roadway adjoining the traveled way for speed change, turning, weaving, truck climbing, maneuvering of entering and leaving traffic, and other purposes supplementary to TH traffic movement.⁽⁶²⁾ Auxiliary lanes are used to balance the traffic load and maintain a more uniform LOS on the highway. They facilitate the positioning of drivers at exits and the merging of drivers at entrances.⁽²⁴⁾
  2. The portion of the roadway adjoining the traveled way for speed change, turning, weaving, truck climbing, maneuvering of entering and leaving traffic, and other purposes supplementary to TH traffic movement.⁽¹²⁶⁾
2. Theoretical/Empirical Effects:
  1. Operational efficiency may be improved by using a continuous auxiliary lane between the entrance and exit terminals where interchanges are closely spaced.⁽²⁴⁾
  2. These can be effectively used to manage traffic but not to necessarily increase capacity.Auxiliary lanes may be used to allow drivers entering roadways additional time to merge into traffic.
  3. Auxiliary lane use by TH vehicles decreases with an increase in right-turning vehicles (RT volume greater than 15 percent of the approach volume renders the auxiliary lane useless to TH vehicles) unless there is a separate RT lane.
  4. Auxiliary lane length, intersection delay, and the proportion of right-turning vehicles work together in determining the utility of an auxiliary TH lane.
  5. For intersections, the HCM default value for the lane utilization factor is 0.91for a three-lane group.⁽¹²⁷⁾
  6. The proper use of auxiliary lanes increases the average speed on freeways, reduces delay on ramps, and reduces the number of conflicts between slow speed and higher speed vehicles.⁽¹²⁸⁾
3. Existing Solutions: Existing solutions include the following:
  1. Build auxiliary lanes.
  2. Increase merging area.
  3. Ensure appropriate lengths for acceleration and deceleration segments.
  4. Provide managed lanes.
4. New Solutions: None reported.

Weaving Areas
1. Description/Definition of the Element: A weaving area is roadway segment where a merge and diverge in close proximity require either merging or diverging vehicles to execute one or more lane changes.⁽¹²⁹⁾
  1. Weaving is generally defined as the crossing of two flows in the same general direction without the aid of traffic control devices.⁽¹³⁰⁾
2. Theoretical/Empirical Effects: Increased lane changing maneuvers creates an increased number of potential conflicts and drivers may reduce speed to accommodate.
  1. The number of lanes is the most critical factor in the determination of the capacity of weaving sections.⁽¹³¹⁾
  2. Shorter weaving sections will begin to break down at relatively lower volumes than longer weaving sections, and weaving speeds fall as weaving volumes increase.⁽¹³²⁾
  3. Total number of lane shifts required by drivers in weaving sections affects both weaving and nonweaving speeds.⁽¹³³⁾
  4. There is no relationship between speed and weaving flow rate in practice.⁽¹³⁰⁾
3. Existing Solutions: Existing solutions include the following:
  1. Minimize weaving impact by lengthening auxiliary lanes and intersection/interchange spacing.⁽¹³⁰⁾
  2. Ramp metering.⁽¹³⁰⁾
  3. Lengthen exit ramps instead of only auxiliary lanes.⁽¹³⁰⁾
  4. Make changes to weaving section type.
  5. Prohibit weaving movement.
  6. Eliminate left-side ramps.
4. New Solutions: None reported.

On-Ramp/Off-Ramp
1. Description/Definition of the Element: An on- or off-ramp is a ramp allowing access to or from a freeway.
2. Theoretical/Empirical Effects: Adding new traffic volume to existing traffic disturbs the flow of vehicles, increases demand, and consequently reduces travel speeds.
  1. Active bottlenecks arise whenever flows from an upstream on-ramp reach a certain peak. Average queue discharge rates were observed to decrease up to five percent than the flows before bottleneck activation.⁽¹³⁴⁾
  2. Discharge flow diminishes when a merge becomes an active bottleneck.⁽¹³⁵⁾
  3. An interchange’s high off-ramp volume, in conjunction with peak-hour arterial flow rates, will cause some intersections to become oversaturated, consequently paralyzing traffic movements along the entire arterial.⁽¹³⁶⁾
  4. An oversaturated arterial adjacent to the interchange can cause off-ramp queue lengths to extend beyond their auxiliary lanes and block the freeway’s mainlines.
3. Existing Solutions: Existing solutions include the following:
  1. On-ramp metering.⁽¹³⁷⁾
  2. Integrate with arterial signal controls.
  3. Maintain proper ramp spacing.
4. New Solutions: None reported.

Acceleration/Deceleration Lanes
1. Description/Definition of the Element: These lanes provide drivers with an opportunity to speed up or slow down in a space not used by high-speed TH traffic.⁽¹²⁸⁾
2. Theoretical/Empirical Effects: Acceleration/deceleration lanes reduce the interference of exiting and entering traffic on main lines and consequently decrease the impact of lane changing maneuvers on freeway speeds.⁽²⁴⁾
  1. Without sufficient length (> 164.04 ft), acceleration lanes decrease stability of main traffic flow due to shock waves (perturbations) in traffic. Longer acceleration lane lengths correlate directly with main traffic stability.⁽¹³⁸⁾
3. Existing Solutions: An existing solution includes the following:
  1. Lengthen/shorten lanes.
4. New Solutions: None reported.

(4) Geometric—Intersections/TCD/ITS

Intersection Sight Distance
1. Description/Definition of the Element: Sight distance is the distance a driver can see at an intersection and can vary according to the driver, obstacles, weather, light, and other conditions.⁽¹⁰⁰⁾
2. Theoretical/Empirical Effects: Intersection sight distance has a strong correlation with vehicle speed.⁽¹³⁹⁾
  1. Decreased sight distance at an intersection leads to less safe conditions for all drivers.
3. Existing Solutions: Existing solutions include the following:
  1. Clear sight triangles.⁽¹⁴⁰⁾
  2. Realign intersection approaches to reduce or eliminate intersection skew.⁽¹⁴⁰⁾
  3. Flat grading.⁽¹⁰⁰⁾
  4. Clearly painted traffic lines.⁽¹⁰⁰⁾
  5. Easily understandable signage.⁽¹⁰⁰⁾
4. New Solutions: A new solution includes the following:
  1. Upgrading to additional, higher intensity, or larger signal heads; backing plates; or modern controllers.

LT and RT Lane Overflow
1. Description/Definition of the Element: LT and RT lane overflow consists of intersections with turn lanes that do not hold all the cars attempting to turn and queue in traffic lanes that are not turning.
2. Theoretical/Empirical Effects:
  1. If the length of a RT lane is inadequate, vehicles waiting to turn may be doing so from the TH traffic lane, thus increasing the potential for rear-end crashes. If long enough, RT lanes provide sheltered locations for drivers decelerating or waiting to make a RT maneuver. Speed is used directly as a measure of mobility, and facilities that emphasize mobility (highways/freeways) accommodate high speed.⁽¹⁴⁰⁾
  2. If a RT lane is excessively long, TH drivers may enter the lane by mistake without realizing it is a RT lane. Effective signing and marking of the upstream end of the RT lane may fix this problem.⁽¹⁴⁰⁾
3. Existing Solutions: Existing solutions include the following:⁽¹⁴¹⁾
  1. LT lanes are designed with adequate storage length, considering both the red-phase queue and leftover queue.
  2. Multiple LT lanes should be provided at an intersection where the LT volume exceeds its capacity and an extreme long LT queue exists.
  3. The length of the LT lane should be extended, or the single LT lane updated to multiple LT lanes, for intersections with LT lane over flow problems to reduce rear-end crash risk.
  4. Longer bay taper lengths should be provided for intersections in the nonurban areas.
  5. Appropriate signal phasing sequence should be adopted to reduce the delay caused by LT.
  6. Single lane TH intersection.⁽¹⁴²⁾
4. New Solutions: A new solution includes the following:
  1. Utilizing electronic pavement marking on roadways to dynamically include bike lanes and dynamically change the width of the lanes.

Parking
1. Description/Definition of the Element: Parking for vehicles may be on the street, in lots, garages, private driveways, and other locations. Time spent looking for parking, as well as the price of parking and its resulting availability, are factors in urban congestion.
  1. Cars looking for parking cause congestion.
  2. Cars parked near intersections.
  3. Double parked cars.
  4. Truck parking/delivery truck parking.
2. Theoretical/Empirical Effects: Improperly priced (or not) parking leads to an inefficient allocation of parking.
3. Existing Solutions: Existing solutions include the following:
  1. Variable pricing/peak pricing/true cost of parking.⁽¹⁴³⁾
  2. Separating parking costs from rent prices and employee benefits.⁽¹⁴³⁾
  3. Parking taxes, targeted or not.⁽¹⁴³⁾
  4. Time limits.⁽¹⁴³⁾
  5. Alternatives—park and rides.⁽¹⁴³⁾
  6. Electronic monitoring in garages and elsewhere (e.g., how many spots are available, also called dynamic parking guidance systems).⁽¹⁴³⁾
  7. Parking cash-out.⁽¹⁴³⁾
  8. Shared parking/park once.⁽¹⁴³⁾
  9. Park-and-ride lots.⁽¹⁴⁴⁾
4. New Solutions: New solutions include the following:
  1. Automated parking technology.
  2. Multilevel parking for each parking spot.

TCDs (Signal, Stop Sign, etc.)
1. Description/Definition of the Element: The purpose of TCDs is to promote highway safety and efficiency by managing the movement of all road users at intersections. Traffic control devices notify road users of regulations and provide warning and guidance needed for the uniform and efficient operation of all elements of the traffic stream in a manner intended to minimize the occurrences of crashes.⁽⁷⁹⁾
2. Theoretical/Empirical Effects: Poor signal design and inadequate/inefficient flow interruption cause delay and vehicles queuing.
3. Existing Solutions: Existing solutions include the following:
  1. Use of real-time or archived data to enhance TCDs.
  2. Properly timed signals.
  3. Effective enforcement.
  4. Actuated signal timing.
  5. Coordinated signal timing along the corridor.
4. New Solutions: New solutions include the following:
  1. Vehicle connectivity.
  2. In-vehicle signal timing display.
  3. Infrastructure-based electronic warning signs.

(5) Operational challenges—Agency Related

Managing Demand
1. Description/Definition of the Element: Managing demand isusing information to promote more efficient use of road capacity.Transportation demand management (also called mobility management) is a general term for strategies that result in more efficient use of transportation resources.⁽¹⁴⁵⁾
2. Theoretical/Empirical Effects:
  1. Demand management can relieve congestion, even if total volume changes are modest. When a road network is at capacity, adding or subtracting even a single vehicle has disproportionate effects for the network.⁽¹⁴⁶⁾
3. Existing Solutions: Existing solutions include the following:
  1. Use of technology:
    1. Electronic toll passes to charge user-fees, including HOT lanes.
    2. Use of real-time and/or archived operations data to adjust toll rates dynamically.
    3. Ramp metering.
  2. Use of incentives/disincentives:
    1. Peak-pricing to encourage shoulder period use.
    2. Daily restrictions (i.e., odd licenses one day).
    3. User-fees (vehicle-miles traveled or other).
    4. Encouragement of transit benefits through taxes or other means.
    5. Raising the gas tax or other indirect fee-for-driving.
  3. Use of alternatives:
    1. Car-sharing.
    2. Park-and-ride lots.
    3. “Guaranteed Ride Home” programs for commuters.
    4. Increased transit options.
    5. Promotion of telework programs.
    6. Express bus service.⁽¹⁴⁷⁾
    7. Special event traffic management.⁽¹⁴⁸⁾
  4. Use of physical barriers:
    1. Traffic-calming devices.
    2. Local traffic only restrictions.
    3. Zone-based pricing bus-only lanes.⁽¹⁴⁹⁾
    4. Express lanes.
4. New Solutions: New solutions include the following:
  1. Smartphone application to orient/manage vehicles routing decision.
  2. Smartphone application to match drivers with riders for carpools.

Intersection Spacing
1. Description/Definition of the Element: Intersection spacing is the minimum distance between intersections on the same side of the street. It is measured by the nearest curb returns on the TH street.⁽¹⁵⁰⁾
2. Theoretical/Empirical Effects:
  1. Having more intersections in closer proximity increases the likelihood of accidents.⁽¹⁵¹⁾
  2. Inadequate TCD and small intersection spacing cause interfering of vehicles queues between consecutive intersections.
3. Existing Solutions: Existing solutions include the following:
  1. Uniform spacing between intersections.
  2. Access roads and other intersection avoidance techniques.
4. New Solutions: None reported.

Interchange Spacing
1. Description/Definition of the Element:
  1. An interchange on an interstate refers to the connections between the interstate and other roadway, which can be another interstate or other lesser roadway. It may include bridges, ramps, and other design features.
  2. Interchange spacing will include the distances between each exit that allows a connection on a limited access road and the spacing within the interchange itself.
2. Theoretical/Empirical Effects: Limiting access speeds traffic and increasing access with more interchanges slows traffic.
  1. Poorly designed interchange spacing can also add confusion to driver behavior.
3. Existing Solutions: Existing solutions include the following:
  1. Uniform interchange spacing as appropriate to specific locations and conditions such as rural areas or urban areas.⁽¹⁵¹⁾
  2. Appropriate signage and facilities to access interchanges.
  3. Longer auxiliary lanes between on- and off-ramps in interchanges.⁽¹²⁷⁾
4. New Solutions: None reported.

Policy on Entry/Exit Ramp Placement—Left Side Versus Right Side
1. Description/Definition of the Element: Exit and entry ramps on interstates are means of accessing and exiting the limited access roads and are typically located on the right side.
2. Theoretical/Empirical Effects:
  1. In design, left exits are not ideal because they do not meet driver expectations, create signing issues, and can create confusion for drivers attempting to exit the highway.⁽¹⁵²⁾
  2. Having exits on the left and right sides on a single road is inconsistent and not a good idea.
  3. Configurations to achieve right-hand entrances and exits could influence ramp-freeway junction locations and, therefore, the ramp spacing between interchanges.⁽¹⁵²⁾
3. Existing Solutions: Existing solutions include the following:
  1. Consistency in use of right-hand exits.
  2. Appropriate signage when using left-hand exits.
4. New Solutions: None reported.

Posted Speed Limit (Static/Dynamic and by Lane Where Applicable)
1. Description/Definition of the Element:Posted speed is the maximum lawful vehicle speed for a particular location as displayed on a regulatory sign.⁽⁸⁸⁾
  1. When no speed is posted, a statutory speed is the lawful limit.⁽⁸⁸⁾
2. Theoretical/Empirical Effects:
  1. The posted speed is established based on an isolated restrictive feature (e.g., sharp curve or limited sight distance) within a segment.⁽⁸⁸⁾ The congestion occurs when the posted speed does not reflect the horizontal/vertical alignment, which leads to form vehicle queues.
  2. Reducing incidence of secondary rear-end crashes.
3. Existing Solutions: Existing solutions include the following:
  1. VSLs.⁽¹⁵³⁾
  2. Traffic calming.
  3. Speed enforcement.
  4. Speed limits based on road conditions that differ based on specific segments rather than the whole road.
  5. Always having a posted limits rather than rely on statutory limits.
4. New Solutions: A new solution includes the following:
  1. Advance queue and lane closure warning (i.e., dynamically drop speed limit incrementally miles upstream of slow or stopped traffic in lane).

Signal Timing Administration
1. Description/Definition of the Element: Signal timing administration includes the coordination of signals for the most efficient use at intersections across a network. It must optimize the intersection for all uses including motor vehicles, pedestrians, and bicyclists as well as transit and freight trains with the goal of increasing flow while decreasing environmental impacts from idle vehicles and dangers.⁽¹⁵⁴⁾
2. Theoretical/Empirical Effects: Poorly timed signals create undue congestion as resources are not being efficiently utilized.
3. Existing Solutions: Existing solutions include the following:
  1. Update signal timing administration annually to evaluate if it is serving existing traffic patterns.⁽¹⁵⁴⁾
  2. Utilization of new technology and control centers.
  3. Signal operation and management.⁽¹⁵⁵⁾
4. New Solutions: A new solution includes the following:
  1. Transit signal priority provides an additional travel time advantage, thereby encouraging transit use.

Challenges due to Traffic Composition
1. Description/Definition of the Element: Traffic composition describes the characteristics of vehicles using a roadway at a given point in time.
  1. Traffic composition usually refers to the percentage of trucks on a roadway but also includes the travel type such as leisure or work-related characteristics.
2. Theoretical/Empirical Effects: Larger and heavier vehicles tend to require more road space and are slower to accelerate. As a result, they cause more traffic congestion than smaller lighter vehicles. The relative congestion impact of different vehicles is measured in terms of passenger car equivalents (PCEs). Large trucks and buses tend to have 1.5–4 PCEs depending on roadway conditions and even more for TH intersections or under stop-and-go driving conditions. A large sport utility vehicle imposes 1.4 PCEs, while a van has 1.3 PCEs when traveling through an intersection.⁽¹⁴⁶⁾
3. Existing Solutions: Existing solutions include the following:
  1. Vehicle restrictions.⁽¹⁵⁶⁾
  2. User fees.
  3. Additional weigh stations to enforce restrictions.
  4. Fewer weigh stations to lessen stopping times.
  5. Peak period restrictions.
  6. Trucks allowed only in right lanes.⁽¹⁵⁷⁾
  7. Weather restrictions.
  8. Strict enforcement and penalties.
4. New Solutions: New solutions include the following:
  1. Use a dynamic tolling for heavy vehicles based on the weight or trip purpose to manage the access of those types of vehicles.
  2. Freight shuttle.⁽¹⁵⁸⁾

Work Zone Administration
1. Description/Definition of the Element: Construction on a roadway causes traffic disturbance, lane closure, speed reduction, and bottlenecks.
2. Theoretical/Empirical Effects: Poor management for a work zone leads to unnecessary speed reduction and reduce the level of comfort for drivers.
3. Existing Solutions: Existing solutions include the following:
  1. Extra lighting.
  2. Warning and advance signage.
  3. Barriers between workers and driving lanes.
  4. Strict speed and driver behavior enforcement including more severe penalties.
  5. Driver education through signage reminding them of workers present.
  6. Use of flaggers.⁽⁷⁹⁾
  7. Use of channelization devices to guide drivers through unfamiliar roadways.⁽⁷⁹⁾
  8. Lane closure policies (e.g., promotion of nighttime/off-peak work to avoid closures during peak traffic volume periods).
  9. Queue warning.⁽¹⁵⁹⁾
4. New Solutions: None reported.

Complete Roadway Closure Administration
1. Description/Definition of the Element: It may be necessary to completely close a roadway for any reason that may include a special event, evacuation, construction, or other event.
  1. Detours direct traffic elsewhere.
  2. Inferred design speed is the maximum speed for which all critical design speed-related criteria are met at a particular location.
2. Theoretical/Empirical Effects: Roadway blockage/closure causes immense delay and reflects on the entire capacity of the network due to the rerouting of vehicles.
3. Existing Solutions: Existing solutions include the following:
  1. Restrictions on vehicle types.
  2. Detour plans in place.⁽¹⁶⁰⁾
  3. Appropriate use of contraflow.
  4. ITS to alert drivers of other routes or changes in roadways.
4. New Solutions: None reported.

Incident Management and Clearance
1. Description/Definition of the Element: In general, many of the traffic congestion sections are caused by some sort of traffic incident, such as a disabled vehicle, a crash, or dangerous driving. Many urban regions have coordinated programs that prevent, identify, and respond to such events quickly and efficiently. These may include centralized traffic management centers, video traffic surveillance, emergency response teams, and even helicopters to move disabled vehicles.⁽¹⁴⁶⁾
2. Theoretical/Empirical Effects: Traffic incidents (disabled vehicles and accidents) account for an estimated 60 percent of delay hours.⁽¹⁴⁶⁾ Although random events, they tend to cause the greatest delays where traffic volumes approach road capacity and so are considered congestion costs. In uncongested conditions, an incident causes little or no traffic delay, but a stalled car on the shoulder of a congested road can produce 100–200 vehicle-h of delay on adjacent lanes.⁽¹⁴⁶⁾
3. Existing Solutions: Existing solutions include the following:
  1. Increased police presence on highways.
  2. Use of ITS to detour and alert drivers.
  3. Incident screens to prevent rubbernecking.⁽¹⁶¹⁾
  4. Solid, integrated freeway traffic management system which can be utilized as a prototype and/or applied in real-time traffic operations.⁽¹⁶⁰⁾
  5. Prepositioned incident response vehicles to clear disabled vehicles in a timely manner.
  6. Aggressive incident clearance programs and policies.⁽¹⁶²⁾
4. New Solutions: None reported.

On-Ramp Management (including ramp metering, etc.)
1. Description/Definition of the Element: Managing traffic on freeway entrance and exit ramps, or ramp management, is the application of control devices, such as traffic signals, signing, and gates, to regulate the number of vehicles entering or leaving the freeway in order to achieve operational objectives. Most ramp management strategies are employed to balance freeway demand and capacity, maintain optimum freeway operation by reducing incidents that produce traffic delays, improve safety on adjacent freeways or arterial streets, or give to a specific section.⁽¹⁶³⁾
  1. Ramp metering is defined as the process of facilitating traffic flow on freeways by regulating the amount of traffic entering the freeway through the use of control devices (such as traffic signals) on entrance ramps. Traffic signals are commonly linked to metering devices, allowing cars to enter the freeway at a predetermined rate.⁽¹⁶⁴⁾
2. Theoretical/Empirical Effects:
  1. Ramp meters control the number of vehicles that can enter a highway ramp. This tends to maintain smoother traffic flow on highways.⁽¹⁴⁶⁾
  2. This strategy may not eliminate traffic congestion but can delay its onset and shorten its duration.⁽¹⁶⁵⁾
3. Existing Solutions: Existing solutions include the following:
  1. Consistent use in roadway design.
  2. Properly timed signals.
  3. Sufficient merging areas including auxiliary lanes.
  4. Effective signage, including dynamic signage.
  5. Bus/HOV queue jump.
4. New Solutions: A new solution includes the following:
  1. Priced queue jump.

Policy for Heavy Vehicles Exclusion on Certain Routes/Lanes
1. Description/Definition of the Element:Larger and heavier vehicles tend to require more road space and are slower to accelerate and, as a result, cause more traffic congestion than smaller, lighter vehicles.⁽¹⁴⁶⁾
2. Theoretical/Empirical Effects: Vehicle restrictions that affect customers with time window constraints do not have an impact on customer costs. However, vehicle restrictions are found to be costly when vehicle capacity is limited.⁽¹⁶⁶⁾
  1. Congestion increases vehicle emissions from heavy vehicles.
  2. Heavy vehicles damage roads.
3. Existing Solutions: Existing solutions include the following:
  1. Restrictions on time and location (peak periods, or on narrow streets).
  2. Strict penalties and enforcement for restrictions.
  3. User fees (heavy vehicles pay for greater damage caused to roads due to weight).
  4. Detector systems for enforcement if weigh stations not in use.
  5. Weigh stations to determination of policy for heavy vehicles.
  6. Detours indicated with signage for heavy vehicles as well as Global Positioning System (GPS) maps with this data included.
4. New Solutions: A new solution includes the following:
  1. Dynamic truck restrictions.⁽¹⁶⁷⁾

Managing Lanes
1. Description/Definition of the Element: Managing lanes includes highway facilities or a set of lanes where operational strategies are proactively implemented and managed in response to changing conditions.⁽¹⁶⁸⁾
2. Theoretical/Empirical Effects:⁽²⁴⁾
  1. Reduce the frequency of collisions caused when motorists encounter congested conditions, work zones, or incidents.
  2. Improve throughput and/or reduce emissions by achieving more uniform and stable traffic flow as demand approaches capacity. This uses the freeway more efficiently and delays or prevents the onset of congestion.
  3. Improve reliability of travel times for certain classes of travelers.
  4. Distribute total delay in a more equitable manner, preserving some capacity for downstream segments.
  5. Increase the efficiency of operation under reduced capacity conditions caused by incidents or maintenance operations.
  6. Divert some freeway traffic to alternative routes or encourage alternative departure times to better use corridor capacity. This will reduce peak-period traffic demand on the freeway.
  7. Provide a travel time incentive to HOVs.
  8. Extend pavement life (by restricting trucks from particular lanes).⁽²⁴⁾
3. Existing Solutions: Existing solutions include the following:
  1. Maintained managed lanes (e.g., working signals, pricing systems, etc.).
  2. Appropriately priced lanes so that lanes are not overused.
  3. Pay-for-use to efficiently allocate use.
  4. Use of data to evaluate successful strategies.
  5. Driver outreach to explain advantages and ways to use managed lanes.
  6. Use of ITS to deliver traveler information, allowing drivers to make informed route, mode, and time of day choices.
  7. HOT/HOV lanes.
  8. Electronic toll lanes.
  9. Congestion/peak pricing.
  10. Reversible lanes.
  11. Transit-only lanes.
4. New Solutions: New solutions include the following:
  1. Mainline metering.⁽¹²³⁾
  2. Green-wave flow techniques.⁽⁴⁰⁾
  3. Priced dynamic shoulder lanes.
  4. In-vehicle technology to allow police to read transponder of vehicles traveling at full speed in adjacent lane. The device reports whether a transponder has had a legal transaction in the past couple of minutes on nonbarrier separated HOT lanes.

Responses to Weather
1. Description/Definition of the Element: Environmental conditions can lead to changes in driver behavior that affect traffic flow. Due to reduced visibility, drivers will usually lower their speeds and increase their headways when precipitation, bright sunlight on the horizon, fog, or smoke are present. Wet, snowy, or icy roadway surface conditions will also lead to the same effect even after precipitation has ended.⁽¹⁶⁹⁾
2. Theoretical/Empirical Effects: Extreme weather can slow traffic and cause accidents with lower sight distances and wet, snowy, or icy conditions. High winds can bring debris into the roadway causing abrupt slowdowns or accidents.Splash and spray from water on the pavement can disorient drivers.⁽¹⁰⁶⁾
3. Existing Solutions: Existing solutions include the following:
  1. Education (e.g., campaigns from emergency management or State to alert drivers to changes due to weather).
  2. Use of ITS especially if putting restrictions into place.
  3. Reflective lighting.
  4. Roadside lighting.
  5. Roadside shelters for pulling over.
  6. Laws with corresponding enforcement and signage (i.e., lights on when raining).
  7. Contraflow for evacuations and law enforcement management.
  8. Salting, putting sand, or other use of material to coat roadway to increase traction.
4. New Solutions: A new solution includes the following:
  1. Restrictions during weather events (e.g., during warnings).

Overheight Management Policy
1. Description/Definition of the Element: These are policies creating guidelines for vehicles over specified heights.
2. Theoretical/Empirical Effects: Vehicles with overheight can cause congestion if they are on a roadway in which clearances are too low. Restrictions can cause overheight vehicles to clog other roadways as well.
3. Existing Solutions: Existing solutions include the following:
  1. Vehicle restrictions.
  2. Strict enforcement and penalties.
  3. Vehicle height detectors.
  4. Signage and warnings.
  5. Time restrictions (i.e., with regard to bridge raisings or other dynamic road conditions).
  6. Plans for alternate routes that aims to distribute large vehicles evenly and safely and not only on small roads not designed for large vehicle traffic.
4. New Solutions: None reported.

Congestion Pricing
1. Description/Definition of the Element: Congestion pricing (i.e., value pricing or zone-based pricing) is a way of harnessing the power of the market to reduce the waste associated with traffic congestion. Congestion pricing works by shifting purely discretionary and lower value peak period highway travel to other transportation modes or to off-peak periods, taking advantage of the fact that the majority of rush hour drivers on a typical urban highway are not commuters. By removing a fraction (even as small as 5 percent) of the vehicles from a congested lane or roadway, pricing enables the system to flow much more efficiently, allowing more cars to move through the same physical space.
  1. Variably priced lanes, involving variable tolls on separated lanes within a highway, such as express toll lanes or HOT lanes.
  2. Variable tolls on entire roadways, both on toll roads and bridges, as well as on existing toll-free facilities during rush hour.
  3. Cordon charges, either variable or fixed charges, to drive within or into a congested area within a city.⁽¹⁷⁰⁾
2. Theoretical/Empirical Effects: Congestion pricing allows the efficient allocation of capacity by charging those who most demand the space to use it and using the principles of supply and demand. It allows planners to price the benefit of less congestion and the true cost of that trip In some cases, may unfairly burden low-income drivers and may not take into account urban to suburban commuting patterns and other nontraditional but common commuting patterns.
3. Existing Solutions: Existing solutions include the following:
  1. Express toll lanes.
  2. Variable pricing/peak pricing/dynamic pricing.
  3. HOT/HOV lanes.
  4. Bus lanes.
  5. GPS systems that allow for distance-based fees.⁽¹⁷¹⁾
  6. “Pay as you drive” insurance programs.⁽¹⁷¹⁾
  7. Use of fees to fund alternatives to driving, such as transit.⁽¹⁷¹⁾
4. New Solutions: New solutions include the following:
  1. Taxes on driving, parking, or types of vehicles.
  2. Tax breaks or incentives for transit use.

Toll Booth Operations
1. Description/Definition of the Element: Toll booths are the facilities in which drivers must pass through when tolls are collected for use of a roadway. They may or may not be staffed or be automated and may have electronic access lanes that accept passes. For facilities where cash tolling is necessary, optimal numbers indicate having twice as many toll booth lanes as traffic lanes.⁽¹⁷²⁾
  1. Toll booth: A shelter where a toll attendant is stationed to collect tolls or issue toll tickets. It is located adjacent to a toll lane and is typically set on a toll island.
  2. Toll island: A raised island on which a toll booth or other toll collection and related equipment are located.
  3. Toll lane: An individual lane located within a toll plaza in which a toll payment is collected or, for toll ticket systems, a toll ticket is issued.
  4. Toll plaza: The location at which tolls are collected. It consists of a grouping of toll booths, toll islands, toll lanes, and, typically, a canopy. Toll plazas might be located on highway mainlines or on interchange ramps. A mainline toll plaza is sometimes referred to as a “barrier toll plaza” because it interrupts the traffic flow.
  5. Toll ticket system: A system in which the user of a toll road receives a ticket from a machine or toll booth attendant upon entering a toll system. The ticket denotes the user’s point of entry. Upon exiting the toll system, the user surrenders the ticket and is charged a toll based on the distance traveled between the points of entry and exit.⁽⁷⁹⁾
2. Theoretical/Empirical Effects:
  1. A car without an electronic pass is delayed 8–12 s at an automatic booth and 13–17 s at a manual booth. Speed is used directly as a measure of mobility. Facilities that emphasize mobility (i.e., highways/freeways) accommodate high speeds.⁽¹⁷²⁾
  2. Cash tolls, by definition, slow traffic, as they must pass through narrow barriers and stop and pay.
3. Existing Solutions: Existing solutions include the following:⁽¹⁷²⁾
  1. Increased use of electronic toll passes or automated tolls booths.
  2. Open road tolling, where all vehicles must either utilize a toll transponder or pay a higher toll receiving a bill in the mail through optical character recognition of the license plate.
  3. Toll booth reconfigurations where vehicles with transponders travel at up to full posted speed in the through lanes and cash toll payers exit to toll booths on the side.
  4. Elimination of physical road barriers.
  5. All electronic tolling.⁽¹⁷³⁾
4. New Solutions: None reported.

Service Patrols Placement
1. Description/Definition of the Element: Service patrols vary by State and locality but generally offer free services to motorists such as providing a gallon of gas, water for an overheated radiator, a cell phone to make a call, as well changing a flat tire or jump starting a car battery. These services are provided using different funding sources and with different personnel, some of which are volunteers, while others are uniformed officers.
2. Theoretical/Empirical Effects: These may get cars off the road sooner but may cause gaper delays.
3. Existing Solutions: Existing solutions include the following:
  1. Larger shoulders.
  2. Larger deployment of service vehicles.
4. New Solutions: A new solution includes the following:
  1. Use of different marked vehicles than law enforcement so as not to create delays associated with seeing law enforcement vehicles.

Law Enforcement Policy/Location
1. Description/Definition of the Element: Highways and roadways often have police units assigned to them to monitor conditions. Law enforcement may take place with parked police vehicles or electronic speed detection, red light cameras, or other method.
2. Theoretical/Empirical Effects: The presence of law enforcement causes slowdowns to avoid moving violations. Areas known for speed traps may be avoided by drivers.
3. Existing Solutions: Existing solutions include the following:
  1. Electronic enforcement of speed and other violations that is indicated by signage.
  2. Elimination of speed traps for revenue-generation only.
4. New Solutions: None reported.

Forecasting Traffic Demand
1. Description/Definition of the Element: Forecasting traffic demand allows transportation practitioners to understand future traffic volumes on their roadways. By analyzing this demand, practitioners can develop and implement improvements (e.g., capacity building or operational strategies) to ensure that the transportation system provides the appropriate LOS to the traveling public.
2. Theoretical/Empirical Effects: Improperly calibrated forecasting tools or poor assumptions may lead to miscalculations on traffic demands and roadway volumes causing practitioners to implement solutions that do not meet the actual need.
3. Existing Solutions: Existing solutions include the following:
  1. Use of ITS to understand regional traffic demand.
  2. Using archived data to calibrate or validate tools or models.
  3. Use of a feedback loop to continually update tools or models.
4. New Solutions: None reported.

(6) Operational challenges—Driver Related

Bunching of Vehicles as a Result of Reduced Speed and Resulting Shockwaves on Abrupt Speed Changes
1. Description/Definition of the Element: In a study carried out by the Organization for Economic Cooperation and Development, a vehicle is regarded as being bunched when it is travelling less than 5 s behind the preceding vehicle and the difference in speed is less than 6.21 mi/h.⁽¹⁷⁴⁾
2. Theoretical/Empirical Effects: The bunching of vehicles is directly causing shock waves and flow disturbance. It might be caused by the changing lanes of heavy vehicles and/or sudden brake by a lead vehicle.
3. Existing Solutions: Existing solutions include the following:
  1. Express buses and buses allowed to make express routes.⁽¹⁷⁵⁾
  2. Use of real-time data to direct detours and inform drivers.
  3. Managed lanes.
  4. Ramp metering.
  5. Dynamic signage and speed limits.
  6. Flat grades and fewer sharp curves.⁽¹⁶⁹⁾
4. New Solutions: None reported.

Roadside Distractions/Rubbernecking
1. Description/Definition of the Element:Roadside distractions include unusual or atypical events that cause drivers to become distracted from driving.⁽¹⁶⁹⁾
  1. Rubbernecking is the act of drivers looking at incidents on the opposite side and causing a delay on the opposite side of the roadway. This can cause accidents as a result.
2. Theoretical/Empirical Effects:Distractions from unusual incidents and rubbernecking often creates slowdowns but also accidents from distracted drivers.
3. Existing Solutions: Existing solutions include the following:
  1. Barriers between traffic flows with higher Jersey barriers or other wall structures.
  2. Screens to prevent drivers from seeing accidents.⁽¹⁶¹⁾
  3. Barriers on roadsides.
4. New Solutions: None reported.

Nonroadside Distractions (i.e., Cellphone Usage, GPS, etc.)
1. Description/Definition of the Element: Distracted driving is anything that takes the driver’s attention from the road including but not limited performing activities not related to driving, using technology, GPS, or interacting with passengers.
2. Theoretical/Empirical Effects: Distracted driving continues to cause more accidents each year.
3. Existing Solutions: Existing solutions include the following:⁽¹⁷⁶⁾
  1. Strict penalties and enforcement.
  2. Education campaigns such as Distraction.gov and through partnerships with mobile phone service providers.
  3. Text stops (like rest stops).
  4. Laws allowing law enforcement to pull over vehicles for distracted driving as a first offense.
  5. Signage.
  6. Use of headsets and restrictions on handheld use and texting bans.
4. New Solutions: A new solution includes the following:
  1. Automatic disabling technology while driving.

Unsafe Vehicle Conditions for Weather Conditions Present
1. Description/Definition of the Element: Weather conditions may present additional hazards for vehicles in poor condition.
2. Theoretical/Empirical Effects: Unprepared/unsafe vehicle conditions can cause sudden stopping actions which will lead to flow disturbance, shockwaves, and a high probability of crashing, especially at poor visibility levels.
3. Existing Solutions: An existing solution includes the following:
  1. Vehicle inspections and requirements.
4. New Solutions: A new solution includes the following:
  1. Electronic enforcement.

Aggressive Driving
1. Description/Definition of the Element: Aggressive driving includes improper driver behavior, including the following behaviors performed poorly:
  1. Lane-changing.
  2. Weaving.
  3. Merging.
  4. Tailgating.
2. Theoretical/Empirical Effects: Aggressive driving can lead to shockwaves, speed reduction, and possible crashes.
3. Existing Solutions: Existing solutions include the following:
  1. Strict penalties and enforcement.
  2. Driver education campaigns, including outreach in communities and through media.⁽¹⁷⁷⁾
4. New Solutions: None reported.

Driving on Unauthorized Roadway Sections (i.e., Unauthorized Shoulder Usage, Median Opening Usage, etc.)
1. Description/Definition of the Element: This includes vehicles and persons driving in areas they are not authorized to drive in.
2. Theoretical/Empirical Effects: Driving on unauthorized roadway section definitely causes flow disturbance and law enforcement.
3. Existing Solutions: Existing solutions include the following:
  1. Signage.
  2. Education.
  3. Penalties and enforcement.
  4. Clear alternatives.
  5. Clearly marked detours, restricted areas, etc.
4. New Solutions: None reported.

Suboptimal Driver Performance in Work Zones
1. Description/Definition of the Element: Motorists alter their driving behavior in work zones compared to when they are traveling in normal freeway conditions.⁽¹⁷⁸⁾
  1. A recent FHWA study showed that drivers who are typically comfortable driving on the freeway are less comfortable when passing through work zones. The study involved a survey in which most drivers reported that they “remain in the same lane while in a construction zone and maintain the speed of the vehicle in front of them.”⁽¹⁷⁸⁾
2. Theoretical/Empirical Effects: Poor driving in work zones can result in damage to cars, people, construction crews, and their equipment. Drivers in heavy construction zones may slow down. Lane decreases and other alterations may cause confusion or congestion.
3. Existing Solutions: Existing solutions include the following:
  1. Traveler information to allow motorists to make more informed decisions (e.g., detour around work zone).⁽¹⁷⁹⁾
  2. Variable message signs.⁽¹⁸⁰⁾
  3. Proper signage, lighting, warning signs, and education.
  4. Clear directives to altered roadways.
  5. Strict enforcement and penalties.
4. New Solutions: None reported.

Suboptimal Driver Performance When Involved in an Incident
1. Description/Definition of the Element: Drivers involved in a minor incident may fail to pull over even when they are able to do so (i.e., there is minimal damage to the vehicle and it is safe to do so), leaving a lane blocked.
2. Theoretical/Empirical Effects: Blocked lane(s) reduce capacity and definitely reduce traffic flow and level of driving comfort.
3. Existing Solutions: Existing solutions include the following:
  1. Signage explaining need to move vehicles from roadway.
  2. Large shoulder on which to move vehicles.
  3. Use of ITS for other drivers.
4. New Solutions: None reported.

Suboptimal Driver Performance on a Roadway with an Incident
1. Description/Definition of the Element: One study found that the reaction time of drivers increases in response to a traffic incident, thus resulting in capacity reductions on highway lanes.⁽¹⁸¹⁾
2. Theoretical/Empirical Effects: The same study noted previously found that capacity per available lane was 30 to 50 percent lower during an incident than under normal conditions due to driver distraction. Similar reductions in flow were found in the opposite direction of the roadway on which an incident occurred.⁽¹⁸¹⁾ Drivers cannot be distracted by events or objects they cannot see. To mitigate rubbernecking in the opposite direction, this statement calls for barriers that block vision to opposite direction traffic conditions. Certain segments along the freeway system could have guardrails and a grass median dividing the freeway traffic.⁽¹⁸²⁾
3. Existing Solutions: Existing solutions include the following:
  1. Faster incident clearance.
  2. Higher barriers between roadways.
4. New Solutions: A new solution includes the following:
  1. GPS data linked to ITS data to provide drivers with choices to take alternate routes.

Suboptimal Driver Performance with Regard to Emergency Vehicles
1. Description/Definition of the Element:
  1. Drivers may slow down and/or get distracted when they hear emergency vehicle sirens but cannot locate the direction the vehicle is coming from.
  2. Drivers may slow down below the design speed limit when they are traveling near a law enforcement vehicle, even if the vehicle is not responding to an emergency.
2. Theoretical/Empirical Effects: Drivers who do not move over or are slow to move over can slow emergency services.
3. Existing Solutions: Existing solutions include the following:
  1. Emergency vehicle preemption uses special control features in traffic signals to provide clear guidance on whether vehicles should stop (providing a red display) or go (providing a green display) at signalized intersections during the approach of emergency vehicles. In these systems, ITS systems attempt to reduce the surprise factor, which may cause drivers to make bad decisions or perform poorly. The benefit of the ITS is the change in the performance of the traffic flow as a result of improved driver behavior.⁽¹⁸³⁾
  2. Larger shoulders for vehicles to pull over.
  3. Properly timed signals that coordinate with emergency vehicles.
  4. irens that can be heard consistently rather than when the vehicle is right behind a vehicle.
  5. Enforcement and stricter penalties for noncompliance.
4. New Solutions: A new solution includes the following:
  1. Interaction with ITS and personal GPS devices as well as automated vehicle guidance systems to alert drivers ahead of time.

Suboptimal Driver Performance with Respect to TCD and ITS Device Operations
1. Description/Definition of the Element: This includes driver misuse of information devices or reactions to the devices.
2. Theoretical/Empirical Effects:Ignoring, misreading, or misinterpreting TCD and ITS devices can lead to poor driving decisions that may negatively impact other drivers or the roadway.
3. Existing Solutions: Existing solutions include the following:
  1. Clear signage.
  2. Maintenance and correct information displayed.
  3. Real-time information.
  4. Strict enforcement and severe penalties.
  5. Red light cameras to enforce traffic signal use.
4. New Solutions: A new solution includes the following:
  1. Integration of GPS mapping with ITS information and TCDs (i.e., GPS directions would alert drivers to upcoming signals, delays, and other roadway information).

Suboptimal Driver Performance with Respect to Usage of Conventional and Alternative Intersections and Interchanges
1. Description/Definition of the Element:
  1. At alternative intersections/interchanges, drivers may slow down because they are unfamiliar with the design of the intersection and uncertain how to proceed through it.
  2. An FHWA study looked at driver behaviors in several different intersection scenarios: red-light running, LTs at busy intersections, turning onto a major road with moderate traffic, and rear-end crashes.⁽¹⁸⁴⁾
2. Theoretical/Empirical Effects:
  1. Reduced speed.
  2. In an FHWA study, for LTs at busy intersection scenario, some younger drivers indicated that they would force their way into the oncoming lane, thereby causing other drivers to slow down or stop.⁽¹⁸⁵⁾
  3. Improper driver behavior at intersections and interchanges can negatively affect other driver’s behavior, cause crashes, confusion, etc.
3. Existing Solutions: Existing solutions include the following:
  1. Advance direction signs (e.g., diagrammatic, stack, and modified stack).⁽¹⁸⁶⁾
  2. Consistent use of signage and roadway design (i.e., right-hand exits).
  3. Driver education with adequate or extra signage to indicate proper behavior.
4. New Solutions: None reported.

Suboptimal Driver Performance with Respect to Pedestrians and Bicyclists
1. Description/Definition of the Element: Drivers may violate traffic rules with regard to other nonvehicle users of the road.
2. Theoretical/Empirical Effects:Either pedestrians or bicyclists can block the roadway, causing congestion or accidents.
3. Existing Solutions: Existing solutions include the following:⁽⁷⁹⁾
  1. Driver education, including campaigns to increase awareness and laws regarding bicyclists and pedestrians (e.g., giving bikers 3 ft).
  2. Proper signage and roadway marking for yielding, crosswalks, bike lanes, parking, and signals for bikers and walk symbols for pedestrians.
  3. Effective road design with the pedestrian rather than only the car in mind.
  4. Consistent enforcement of violations.
  5. Pedestrian refuges and barriers from car traffic for bicyclists, as well.
4. New Solutions: A new solution includes the following:
  1. Strict penalties and enforcement for those violating and negatively impacting pedestrians and bicyclists, including criminal proceedings as would take place in injuries relating to vehicle accident. Criminal charges are rarely filed for drivers hitting pedestrians on sidewalks.

Suboptimal Driver Performance with Respect to Animal Crossings
1. Description/Definition of the Element: Animals in the roadway can cause accidents and slowing of traffic. Additionally, it is often harmful to species, as they can be severely injured or killed.
2. Theoretical/Empirical Effects: Animals in the roadway can cause gaper delays, slow-downs, and accidents, as well as loss of life for animals attempting to cross the road.
3. Existing Solutions: Existing solutions include the following:
  1. Signage indicating need for extra vigilance.
  2. Fences to keep wildlife at bay.
  3. Designated wildlife crossings and bridges that, while expensive, recognize the importance of wildlife in their habitat that has been interrupted by a roadway. These can include bridges, overpasses, culverts, and other physical structures meant to guide animals to safety.⁽¹⁸⁷⁾
4. New Solutions: None reported.

Suboptimal Driver Performance with Respect to Commercial and Heavy Vehicle Operation
1. Description/Definition of the Element: This constitutes violation of traffic rules and norms by commercial and heavy vehicles operation either by drivers of commercial and heavy vehicles or by drivers interacting with them.
2. Theoretical/Empirical Effects: Accidents and congestion can result from improper behavior by drivers of these vehicles or by drivers around them.
3. Existing Solutions: Existing solutions include the following:
  1. Effective enforcement.
  2. Restrictions on roadways and timing (i.e., delivery only at night).
4. New Solutions: None reported.

(7) Operational Challenges—NonMotorist Related

Suboptimal Pedestrian and Bicyclist Performance
1. Description/Definition of the Element:Pedestrians and bicyclists may violate traffic rules.
2. Theoretical/Empirical Effects:They can either block the roadway and cause congestion or result in accidents possibly with injuries to the pedestrians and bicyclists.
  1. Sharing the road with cars slows cars down.
3. Existing Solutions: Existing solutions include the following:⁽⁷⁹⁾
  1. Working walk symbols with properly timed countdowns in marked crosswalks and signage indicating pedestrians present.
  2. Designated bike lanes, especially separate from the roadway, but clearly marked, and signage indicating bicyclists sharing the roadway or are present.
  3. Enforcement to penalize and discourage violation of traffic rules and equipment requirements such as helmets, reflectors, and lamps.
  4. Pedestrian refuges in large road crossings.
  5. Effective roadway design.
  6. Complete streets where roadways are designed or redesigned with all users in mind rather than strictly vehicles.
  7. Requiring bicyclists to be registered so if they are ticketed they will have a record.⁽¹⁸⁸⁾
  8. Media campaigns about sharing the road and pedestrian and bicyclist laws and behavior.
  9. Retiming anarterialstreet to achieve pedestrian access.
4. New Solutions: A new solution includes the following:
  1. Separate bike-only lanes between parking and sidewalk or part of sidewalks, as in many European countries.

Page Owner: Office of Research, Development, and Technology, Office of Infrastructure, RDT

Topics: research, infrastructure, structures
Keywords: research, structures, Accelerated bridge construction, prefabricated bridge elements, grout-like materials, dimensional stability, shrinkage, internal curing.
TRT Terms: research, infrastructure, Facilities, Structures
Scheduled Update: Archive - No Update needed

This page last modified on 02/21/2017