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Roadway Geometry and Inventory Trade Study for IntelliDrive^SM Applications Applications

CHAPTER 4. SUMMARY OF ROADWAY DATA AVAILABILITY

This chapter examines the current and potential availability of each roadway geometry and inventory data item identified by IntelliDrive stakeholders based on the review of current roadway data sources and emerging data collection technologies. The chapter is divided into four subsections, each corresponding to one of the four general data categories used throughout this report: roadway geometry, roadway inventory, intersection characteristics, and other geospatial features.

Each subsection includes a table that summarizes the relative availability of each roadway data item from current data sources and with extensive deployment of emerging data collection technologies. A comments column provides additional information on current and potential data availability.

ROADWAY GEOMETRY

Table 14 summarizes the current and potential availability of each roadway geometry data item identified by IntelliDrive stakeholders.

Horizontal curvature, grade, and elevation are data items that are currently being collected by two of the commercial roadway network developers, NAVTEQ™ and Tele Atlas^®, as part of their ADAS supplement to their core roadway network databases as well as by approximately half of the State DOTs who responded to the survey.

Both NAVTEQ™ and Tele Atlas^® derive measures of horizontal curvature (radius and curve length) and grade directly from the geographic coordinates (latitude, longitude, and absolute elevation) of the shape points used to draw their roadway networks. NAVTEQ™ includes measures of curvature and grade only on roadway segments that meet its enhanced locational accuracy standards for ADAS. Tele Atlas^® calculates measures of curvature and grade for all roadway segments but acknowledges that there may be significant inaccuracies in these measures for road segments that do not meet its ADAS locational accuracy standards. Both NAVTEQ™ and Tele Atlas^® indicated that all of their class 1 and 2 roads are currently ADAS-compliant. These road classes generally correspond to roads functionally classified as interstates, freeways and expressways, and other principal arterials.

Table 14. Availability of roadway geometry data.

NAVTEQ™, Tele Atlas^®, and about 25 percent of the State DOTs reported that they collect vertical curvature on some roads, but the data collected by these sources do not quite match the data needs identified by IntelliDrive stakeholders. Both NAVTEQ™ and Tele Atlas^® reported that they measure vertical curvature as the change in slope between shape points along a road segment and measure grade as the average slope (Δelevation/Δhorizontal distance) between the two endpoints of a roadway segment. Both NAVTEQ™ and Tele Atlas^® collect vertical curvature data for ADAS compliant road segments.

Although both NAVTEQ™ and Tele Atlas^® plan to expand the number of ADAS-compliant roads in their roadway databases to include class 3 and 4 roads, it is highly unlikely that they will be able to collect enhanced horizontal and vertical alignment data on class 5 (local) roads in the near future. Since local roads comprise nearly 70 percent of total U.S. roadway centerline miles, some other data collection method will have to be utilized to provide accurate horizontal and vertical alignment data for these roads. IFSAR technology, described in the previous chapter, could produce a national 3 D roadway centerline database with consistent levels of horizontal and vertical accuracy for all roads. However, there are at least three unresolved questions concerning IFSAR: (1) Are the levels of accuracy claimed by the technology developer independently verifiable? (2) Do these accuracy levels meet the needs for IntelliDrive applications? (3) Who would pay for the processing of IFSAR data to create a national 3 D roadway centerline database?

None of the commercial roadway database developers and virtually none of the State DOTs currently collect data on roadway or shoulder cross slope. Moreover, none of these data items are currently required for HPMS reporting, even for sample sections. Although it is technologically feasible to collect each of these data items, especially with new mobile LIDAR, it is highly unlikely that these data will be available for IntelliDrive applications in the near future.

Sight distance is another attribute that is not routinely collected by commercial roadway database developers or most State DOTs as part of their roadway inventories. HPMS includes passing sight distance as a sample section data item but defines it as the percent of a sample segment length that allows passing.

ROADWAY INVENTORY

Table 15 summarizes the current and potential availability of each roadway inventory data item identified by IntelliDrive stakeholders.

Data on the number of lanes for each roadway segment and on median and ramp locations along divided highways are currently available from commercial roadway database developers for most roads in their databases.

More specific data on the characteristics of lanes, medians, shoulders, and ramps, including type and special use or restrictions (e.g., HOV, no trucks) are routinely collected by State DOTs as part of their roadway inventories. State DOTs do not typically measure actual lane width on a multilane road. Instead, they compute an average lane width based on the total paved width of the travel way and the number of lanes. None of the commercial roadway database developers and virtually none of the State DOTs currently collect data on clear zone width.

Because most State DOTs only inventory those roads for which they have maintenance responsibilities, roadway inventory data are available primarily for higher functional class roads that are part of the State highway system. HPMS includes many of these attributes as sample section data items. Only the number of lanes on roadways and ramps and designated HOV lanes are required for all HPMS road segments.

Table 15. Availability of roadway inventory data.

Both commercial roadway databases and State DOTs include posted speed limit as a data item. Speed limit data are likely to be more accurate and current on higher functional class roadways and may be more spotty on local roads that are outside the maintenance responsibility of State DOTs or that are surveyed less frequently by commercial database developers. Data on special speed zones or advisory speeds vary from State to State, and to the extent that many special speed zones are located on local streets (e.g., school zones), these data may not be routinely collected or compiled on a statewide basis.

Data on guardrail locations and type are currently not collected by commercial roadway database developers, and most State DOTs do not maintain centralized inventories of guardrails, signs, pavement markings, or roadside lighting. Instead, inventory and maintenance responsibilities for these roadway features are typically delegated to individual maintenance districts dispersed geographically across the State.

Both NAVTEQ™ and Tele Atlas^® collect data on longitudinal pavement markings for those roads with enhanced lane information. Generally, these roads include ADAS-compliant road segments, plus roads that are in selected urban areas and enter complex intersections where additional lane guidance is needed. Most State DOTs do not maintain a centralized inventory of pavement markings.

Data on sidewalk locations are not routinely collected by commercial database developers or State DOTs. One reason is that most State highway system roads are located outside of urban areas and typically do not have sidewalks or do not permit pedestrian traffic (e.g., interstates). Both NAVTEQ™ and Tele Atlas^® include some information on sidewalks in their Discover Cities™ and Urban Maps™ supplemental data products, but these products are only available for selected larger U.S. cities.

All of the listed roadway inventory data items can be collected using either videologs or LIDAR technology mounted on mobile roadway data collection vehicles. Many State DOTs are already using such technologies to collect specific data items for their State highway system. However, the data processing costs to extract and inventory each roadway feature make it highly unlikely that these data will be available for all roads without some financial incentive or regulatory mandate.

INTERSECTION CHARACTERISTICS

Table 16 summarizes the current and potential availability of each intersection characteristic data item identified by IntelliDrive stakeholders.

Table 16. Availability of intersection characteristics data.

Data on intersection location and type, as well as restrictions on specific turning movements, are currently available from commercial roadway database developers for most, if not all, roads in their databases. These items are critical to vehicle navigation and routing and are therefore maintained and updated by commercial developers as high-priority data items.

Other lane configuration attributes, including location and number of dedicated turn lanes and lane channelization, are also available from NAVTEQ™ and Tele Atlas^® for those intersections where enhanced lane information is provided. Currently, these data items are available for class 1 and 2 roads nationwide and for class 3 and 4 roads (collectors and minor arterials) located in larger cities. Both NAVTEQ™ and Tele Atlas^® plan to increase the number of U.S. cities where such enhanced lane data are available. Neither commercial developers nor State DOTs currently collect measured lane widths for turning lanes or allowable vehicle paths through an intersection.

Most State DOTs do not collect detailed data on intersection characteristics beyond what is required for HPMS reporting. HPMS requires only a summary measure of turning movements along a sample section, indicating whether any intersections exist along the sample section, and if so what turning movements, if any, are permitted.

Data on the location of pedestrian crosswalks are available from NAVTEQ™ and Tele Atlas^® for selected cities in their Discover Cities™ and Urban Maps™ supplemental data products. As with their extended lane data, both developers plan to increase the number of U.S. cities where such information is available. None of the State DOTs reported that they collect data on crosswalks or other pavement markings in urban areas.

Data on the location and type of traffic control (i.e., sign or traffic signal) at intersections is available from both NAVTEQ™ and Tele Atlas^®. The level of detail and locational accuracy of these data varies depending on whether enhanced lane information has been collected for the intersection.

Relatively few of the State DOTs maintain a centralized traffic signal or sign inventory beyond what is required for HPMS reporting. HPMS requires only a total count of the number of intersections along a sample section that are controlled by traffic signals or stop signs.

All of the listed intersection characteristics data items can be collected using either videologs or LIDAR technology mounted on mobile roadway data collection vehicles. However, the data processing costs to extract and inventory each roadway feature make it highly unlikely that these data will be available for all roads without some financial incentive or regulatory mandate.

None of the commercial roadway database developers and few, if any, State DOTs currently collect data on whether the signal supports transit priority or preemption for emergency vehicles. This type of operational data may be collected by specific TMCs that have operational control over traffic signals within their service area, but it is not likely to be available in a roadway database anytime in the foreseeable future.

OTHER GEOSPATIAL FEATURES

Table 17 summarizes the current and potential availability of other geospatial features identified by IntelliDrive stakeholders.

Data on the locations of highway railroad crossings, bridges, and tunnels, along with most of the characteristics of these features required for IntelliDrive applications are currently available in commercial roadway databases and from national inventory databases compiled and maintained by the U.S. DOT. Commercial roadway network database developers, especially those that support commercial trucking customers, update height and weight clearances and commercial vehicle restrictions on a priority basis using a variety of sources, including contacts with State and local transportation agencies, customer feedback, and direct observation by field teams.

Most public transit operating agencies collect and maintain data on their transit stop locations. Both NAVTEQ™ and Google™ have collected transit stop locations from many U.S. transit agencies and have included them as a geospatial feature layer for use with their roadway database.

Several of the commercial roadway databases, including NAVTEQ™, Tele Atlas^®, and ALK^®, collect data on the locations of truck rest areas and roadside inspection/weigh stations on major truck routes for use with their commercial vehicle data products. Additional data on the characteristics of truck-related facilities (e.g., capacity and amenities at truck stops) are not currently included in these databases. Most State DOTs do not maintain inventory data on commercial vehicle facilities.

Table 17. Availability of other geospatial features.

Geographic features that define coverage areas for specific information services, which may be useful for IntelliDrive applications, currently do not exist on a nationwide basis. Moreover, such coverage area maps may not be particularly informative as part of a roadway database. At least two of the services, weather monitoring and enhanced GPS, have or will soon have ubiquitous coverage throughout the United States. Road condition monitoring is currently being deployed by individual State DOTs for their entire States, and traffic monitoring is currently being deployed as a partnership between commercial roadway databases developers and traffic monitoring services, with traffic updates integrated directly into the roadway database on individual road segments.

Differential GPS coverage is currently available for most of CONUS, Hawaii, Puerto Rico, and coastal Alaska. A GPS receiver equipped with differential GPS capability can improve the accuracy of its positional readings from 32.8 ft (10 m) to less than 3.28 ft (1 m) absolute error. Currently, however, most vehicle-installed and handheld navigation systems are not equipped with differential GPS capability.

The National Differential Global Positioning System (NDGPS) program, which is managed by the U.S. DOT, is expected to add eight additional base station sites to achieve full CONUS coverage. The schedule for construction of these new sites depends on availability of funding. The U.S. Coast Guard Navigation Center maintains a map showing current differential GPS coverage areas.⁽⁸⁾ This map could be made available as a geospatial feature for use with a roadway database. No State or nationwide databases were found showing the locations of areas with especially poor GPS coverage, such as natural or urban canyons.

The National Weather Service has developed and maintains the National Digital Forecast Database (NDFD), which provides current and future forecasts of weather conditions throughout the United States.⁽⁹⁾ The NDFD is updated on an hourly basis for most attributes and can be accessed and displayed for any U.S. location at a geographic resolution of 3.1 mi (5 km) grids. These data are currently used by many TMCs and State DOTs as the basis for monitoring weather conditions within their service area.

Many of the commercial roadway database developers have established partnerships with traffic monitoring services to provide near-real-time traffic conditions as a supplemental roadway attribute. Traffic monitoring coverage is not consistent nationwide and tends to be concentrated in larger metropolitan areas with correspondingly higher levels of traffic congestion. No State or nationwide databases were found that showed the coverage area boundaries of traffic monitoring services. Moreover, these boundaries appear to be relatively fluid and may not be suitable for display on a static map.

Several State DOTs have developed public traveler information services (e.g., 511) Web sites that provide a variety of information on roadway conditions, work zones, traffic conditions, and roadway weather conditions. Information is updated throughout the day as conditions change.

Although State DOT sites are typically limited to information pertinent to State roads, these sites can provide the framework for additional information provided by local transportation agencies for roads in their service area.