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Federal Highway Administration Research and Technology
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Publication Number: FHWA-HRT-10-073
Date: November 2010

Roadway Geometry and Inventory Trade Study for IntelliDriveSM Applications Applications



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 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.


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.



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 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)


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.



Attribute Definition


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 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 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 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)


Location of sidewalk

Start and end of sidewalk relative to the roadway in the direction of travel (including left/right side)


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.



Attribute Definition


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


U-turn prohibition


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


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?


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.



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


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


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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