Roadway Geometry and Inventory Trade Study for IntelliDriveSM Applications Applications
CHAPTER 2. INTELLIDRIVE DATA NEEDS
PRELIMINARY LIST OF ROADWAY DATA ITEMS
A complicating issue in conducting this trade study is that few, if any, IntelliDrive applications have been defined in sufficient detail to specifically identify what data items or what levels of geospatial accuracy are needed to support them. Both IntelliDrive applications and data requirements are still evolving, and it is likely that early IntelliDrive applications will be driven heavily by data availability.
Recognizing that both data needs and applications will continue to evolve, a preliminary list of roadway geometry and inventory data was developed jointly by U.S. DOT staff and the study team. This initial list was compared against roadway data elements identified in several other similar research studies, including the Enhanced Digital Mapping Project, Model Minimum Inventory of Roadway Elements—MMIRE, and SHRP2 Project S-03—Roadway Measurement System Evaluation.(1,2)
The combined lists of roadway data items from these sources were then evaluated against an initial set of IntelliDrive application areas that FHWA and other U.S. DOT staff identified as candidates for deployment. These application areas included the following:
- Roadway departure prevention.
- Speed management.
- Intersection safety.
- Commercial vehicle enforcement and operations.
- Transit.
STAKEHOLDER OUTREACH PROCESS
Stakeholder outreach was conducted to ensure that the preliminary list of roadway geometry and inventory data addressed the needs of IntelliDrive stakeholders. Potential stakeholders were identified based on their involvement in the IntelliDrive Coalition, the American Association of State Highway and Transportation Officials (AASHTO) IntelliDrive Technical Working Group, the Crash Avoidance Metrics Partnership (CAMP), and other groups. Representatives from State and local transportation departments, transit agencies, automobile manufacturers, the motor carrier industry, traffic signal and other electronic infrastructure manufacturers and suppliers, traffic management system integrators, university transportation research centers, and other IntelliDrive integrators/developers were included. A list of the organizations represented by potential stakeholders is presented in appendix A.
The study team attempted to recruit one representative from each of the organizations identified on the stakeholder list. For organizations with multiple contacts, the study team initially contacted one person and proceeded to contact other individuals only if the initial contact was unable or unwilling to participate. In some cases, the initial point of contact referred the team to another individual who was more familiar with the technology and data issues associated with IntelliDrive applications or who was more readily available to participate in stakeholder meetings. The stakeholder list was updated accordingly throughout the stakeholder outreach process.
Stakeholder outreach was conducted through three Web meetings, which took place November 18–20, 2009. Meetings with stakeholders were scheduled and coordinated via email and Doodle®, an online collaboration application. Of the 75 stakeholders who received an invitation email, 30 participated in the Web meetings. The preliminary list of roadway data items was sent to all stakeholders for review prior to the meetings. The data items were mapped to a list of potential IntelliDrive applications to facilitate stakeholder responses.
REVISED ROADWAY DATA ITEM LIST
The feedback obtained during the stakeholder meetings was used to revise the preliminary list of roadway geometry and inventory data needs. Appendix B presents a summary of key comments raised by various IntelliDrive stakeholders during the meetings.
Most of the comments and suggestions raised by stakeholders were incorporated into a revised list of roadway geometry and inventory data items. A few recommended data items were left off the revised list because they did not fit within the scope of this study or were combined with similar data items to create a single attribute or feature.1 The affected data items included:
- Traffic and railroad crossing signal status. These two attributes describe the real-time status of a dynamic traffic control device (e.g., is the traffic signal currently red or green?). While these data may be needed for certain IntelliDrive applications, they are too dynamic to be maintained in a roadway geometry database, which contains geospatial features and attributes that are relatively static over time or which change in regular, predictable ways (e.g., reversible high-occupancy vehicle (HOV) lanes). Additionally, traffic signal phase and timing data are currently included as a proposed message layer in the Cooperative Intersection Collision Avoidance System Dedicated Short Range Communication (DSRC) message protocol. Consequently, these two data items were deleted from the revised list.
- Pavement coefficient of friction. Pavement coefficient of friction is another measure that changes dynamically, depending on weather conditions, roadway surface type (e.g., concrete, asphalt, gravel), roadway pavement condition, and vehicle speed. While most State DOTs collect data on pavement surface type and condition, none of them specifically maintain coefficient of friction as a roadway inventory item. Consequently, pavement coefficient of friction was excluded from the revised list, and a pavement type attribute was added as a placeholder pending future identification and specification of the key roadway pavement data items (e.g., surface type, condition) needed to calculate a coefficient of friction.
- Horizontal and vertical sight distance. Available sight distance is a measure that is based on a combination of horizontal and vertical alignment of the roadway ahead of a vehicle and any lateral obstructions along the roadside. Consequently, sight distance was combined into a single roadway geometry feature/attribute.
- Superelevation and roadway cross slope. The terms superelevation and roadway cross slope both describe a measure of roadway slope that is perpendicular to the centerline of the roadway. Although superelevation is typically used in conjunction with a horizontal curve, it is not measured differently nor stored independently from cross slope. Consequently, superelevation was consolidated into the more general roadway cross slope attribute.
Table 1 through table 4 present the revised list of roadway geometry and inventory data items. Data items are grouped into four general categories for presentation purposes: roadway geometry, roadway inventory, intersection characteristics, and other geospatial features. These categories are used throughout the remainder of this report.
Table 1. Roadway geometry attributes.
Feature |
Attribute |
Attribute Definition |
Horizontal alignment |
Horizontal curve PC location |
Location where curve begins |
Horizontal curve length |
Length of curve along arc defined by roadway |
Horizontal curve radius |
Radius of curve |
Grade |
Grade in direction of travel |
Percent of slope measured in direction of travel. (Positive (+) for uphill in direction of travel and negative (-) for downhill in direction of travel) |
Elevation |
Roadway elevation |
Elevation of the roadway centerline above a specified geodetic reference point. |
Vertical alignment |
Vertical curve PC location |
Location where curve begins (including elevation) |
Vertical curve PT location |
Location where vertical curve ends (including elevation) |
Vertical curve length |
Length of curve along arc defined by roadway |
Sight distance |
Available sight distance (stopping, passing) |
Available sight distance along the roadway in direction of travel |
Cross slope |
Roadway cross slope |
Percent of slope measured from highpoint of roadway cross section in direction of travel. (Positive (+) slopes toward right side of road and negative (-) slopes towards left side of road) |
Shoulder cross slope |
Cross slope of shoulder. Direction and percent of cross slope measured from the edge of travel lane to edge of pavement |
Table 2. Roadway inventory attributes.
Feature |
Attribute |
Attribute Definition |
Roadway |
Number of through lanes |
Number of continuous through lanes on road segment |
Roadway use restrictions |
Vehicle restrictions that apply to the entire road segment (e.g., no trucks, HOV/HOT, height or weight limits, HAZMAT, tolled, etc.) |
Roadway surface type |
Type of roadway surface or pavement (e.g., dirt, gravel, asphalt, concrete) |
Lane |
Lane number |
Integer value indicating which lane in a roadway segment attributes apply (by convention, lanes are counted outward from the center of the roadbed in the direction of travel (e.g., left to right in United States) |
Lane width |
Measured width of lane |
Special lane function type |
Special lane function type (e.g., left-turn lane, HOV/HOT lane, bicycle lane, reversible lane, bus bay, tolled, etc.) |
Lane pavement marking location |
Location of pavement marking relative to lane in direction of travel (e.g., left, right, inside) |
Lane pavement marking type |
Type of longitudinal pavement markings (roadway edge, solid centerline, dashed, “diamond” lane) |
Median |
Median location |
Start and end of median relative to the roadway in the direction of travel |
Median type |
Soil, paved (striped), paved (barrier), raised curb, other |
Median width |
Average width of median |
Shoulder |
Shoulder location |
Start and end of shoulder relative to the roadway in the direction of travel (including left/right side) |
Shoulder type |
Paved, unpaved, composite (part paved, part unpaved), and curb |
Shoulder width |
Width of paved portion of shoulder, measured from edge of travel lane to edge of paved surface |
Clear zone width |
Measured from edge of travel lane to either a fixed obstacle, or nontraversable slope ( > 1:3) |
Special shoulder function type |
Special shoulder use (e.g., queue bypass lanes for HOV or transit, peak-period travel lane) |
Sidewalk |
Location of sidewalk |
Start and end of sidewalk relative to the roadway in the direction of travel (including left/right side) |
Ramp |
Ramp location |
Location of gore point of ramp |
Ramp type |
Entry, exit, freeway-to-freeway (in direction of travel) |
Ramp number of lanes |
Number of continuous through lanes on ramp |
Ramp merge feature |
Acceleration or deceleration lane |
Ramp special lane function type |
Special lane function on ramps (e.g., queue bypass lane for HOV or transit) |
Speed zone |
Speed zone location |
Start and end of speed zone relative to roadway |
Posted speed limit |
Posted speed within speed zone |
Posted advisory speed |
Posted advisory speed on curves |
Special speed zone type |
Type of special speed zone (e.g., school zone, work zone, differential speed limits for trucks, variable speed limits, by lane, if applicable) |
Roadside barrier (guardrail) |
Barrier location |
Start and end of barrier relative to the roadway in the direction of travel (including left/right side) |
Barrier type |
Cable, guardrail, concrete barrier, other |
Table 3. Intersection characteristics.
Feature |
Attribute |
Attribute Definition |
Geometry |
Intersection location |
Location of center and corners of intersection |
Intersection ID |
Global identifier that indicates the operating agency and unique identification number of the intersection |
Type of intersection |
X-intersection, T-intersection, Y-intersection, roundabout, more than 4 intersecting segments |
Approach lane configuration |
Number of through lanes |
Number of through lanes on approaching road segment |
Lane width |
Individual widths for through and turn lanes |
Left-turn prohibition |
Yes/no |
U-turn prohibition |
Yes/no |
Number of left-turn lanes |
Number of exclusive left-turn lanes |
Location of left-turn lane |
Location of start of the left-turn lane on approaching road segment |
Left-turn channelization |
Are left-turn lanes physically separated by curb or positive barrier? |
Right-turn prohibition |
Yes/no |
Number of right-turn lanes |
Number of exclusive right-turn lanes |
Location of right-turn lane |
Location of start of the right-turn lane on approaching road segment |
Right-turn channelization |
Are right-turn lanes physically separated by curb or positive barrier? |
Vehicle paths through intersection |
Centerline and route of all available vehicle paths through the intersection |
Pavement markings |
Location of stop bar |
Location of left and right edge of the stop bar on approach |
Location of pedestrian crosswalk |
Location of edge of marking nearest to the vehicle |
Location of midblock pedestrian crosswalk |
Location of edge of marking nearest to the vehicle |
Traffic control |
Type of traffic control |
Signalized, stop sign, yield sign, none |
Location of traffic signal |
Location of traffic signal head |
Traffic signal preemption |
Is traffic signal preemption provided for emergency vehicles at signalized intersection? |
TSP |
Is TSP provided for emergency vehicles or transit vehicles at signalized intersection? |
Special traffic control |
Special traffic control for buses, BRT (e.g.,queue jump in right-turn lane), mixed traffic (i.e., light rail transit vehicles and autos) |
Table 4. Other geospatial features.
Feature |
Attribute |
Attribute Definition |
Rail crossings |
Railroad crossing location |
Position of first rail of first track at at-grade railroad crossing |
Railroad crossing control type |
Type of crossing control (e.g., sign, pavement marking, signal, gates) |
Railroad crossing identifier |
U.S. DOT inventory crossing number |
Bridges/
tunnels |
Bridge/tunnel location |
Start and end of bridge/tunnel relative to the roadway in direction of travel |
Structure type |
Bridge, tunnel traversed by roadway, bridge crossing over roadway |
Overhead clearance |
Actual and posted clearance height of structure crossing over a roadway |
Restrictions |
Height or weight limits |
Bridge identifier |
NBI number |
Transit facilities |
Transit stop location |
Location of bus stop |
Transit stop type |
Type of bus stop, such as in-lane, pulloff lane, counterflow pullout |
Commercial vehicle facilities |
Truck parking facility location |
Location of truck parking facility (public and private) |
Truck parking facility capacity |
Number of trucks allowed to park at facility |
Roadside inspection/weigh station location |
Location of roadside inspection/weigh stations |
Runoff lane location |
Location of runoff lane for trucks |
GPS coverage |
GPS coverage area location |
Boundaries of areas where GPS coverage is enhanced or limited |
GPS coverage area type |
Type of GPS coverage (e.g., GPS coverage limited by terrain, structures, or other factors, or enhanced NDGPS coverage available) |
Weather monitoring coverage |
Weather monitoring coverage area location |
Boundaries of areas where local weather monitoring station data are transmitted to motorists |
Road condition monitoring coverage |
Road condition monitoring coverage area location |
Boundaries of areas where real-time information on road conditions is transmitted to motorists |
Traffic monitoring coverage |
Traffic monitoring coverage area location |
Boundaries of areas where real-time information on local traffic conditions is transmitted to motorists |
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