Geometric Design Resources

The 2021 ITE Developing Trends Report represents collective input from ITE Councils and Standing Committees on emerging transportation challenges and solutions. The report covers transportation planning, engineering, management, and operation advancements and will benefit the industry's leaders and professionals in the public and private sectors. The Developing Trends Report Task Force reached out to all ITE Councils and Standing Committees to identify trends relevant to their scope and expertise.

Convener: Marvin Ta, Pennoni

Convener: Randy McCourt

Convener: Patrick Wright, Pennoni

Convener: Murray Allen, Marr Traffic and Mark Lenters, Kimley-Horn

Convener: Marvin Ta, Pennoni & Associates

Convener: Matthew Ridgeway, Fehr and Peers

Convener: Patrick Wright, PennDOT's Local Technical Assistance Program

Convener: Patricia Tice, University of Central Florida

Conveners: Aaron Lockwood, Carmanah Technologies and Melisa Finley, TTI

According to the Federal Highway Administration (FHWA), in 2008 nearly one-fourth of the fatalities occurred at horizontal curves. Particularly, fatality rates at rural horizontal curves are more than twice than that at urban horizontal curves. Fatal-and-injury (FI) (i.e., incapacitating injury crash, non-incapacitating crash, and possible injury crash) crashes accommodate roughly half the number of total crashes. Hence, addressing the safety problem at horizontal curves is one of FHWA's three focus areas. The Strategic Highway Safety Plan prepared by the American Association of State Highway and Transportation Officials (AASHTO) also counts crashes at horizontal curves as one of 22 emphasis areas.

Intersections are recognized as the most hazardous locations on roads since conflict possibilities are high at intersections. This often results in a high frequency of fatal and severe crashes at intersections. Although intersections constitute only a small proportion of the entire roadway system, a significantly high proportion of crashes are reported at intersections. More than 50 percent of the combined fatal and injury crashes occur at or near intersections. More than 9,000 people lose their lives in intersection crashes every year in United States. Many of these fatal and severe intersection crashes are reported at right-turns and are predominantly attributed to wide angle, sweeping, high-speed, right-turns.

Transportation engineers are facing great challenges in meeting the mobility demands of an increasing population. As traffic demands continue to rise at many highway junctions, motorists, pedestrians, and bicyclists all experience longer delays and greater safety risks. Today's traffic problems are very complicated, and conventional intersection designs are often found to be insufficient to alleviate them. As a result, various innovative intersection designs are being investigated and implemented to mitigate or solve these complex problems.

The Minnesota Department of Transportation (MnDOT), cities, counties, and the consultant community have made great strides in utilizing a broader range of intersection types to solve transportation problems in Minnesota. By the end of the 2018 construction season, MnDOT and local agencies will have constructed 29 restricted crossing U-turn (RCUT) intersections, six diverging diamond interchanges (DDI), two continuous Green T intersections, and more than 100 roundabouts.

Urban Street Geometric Design Handbook - Errata

This AASHTO guide provides a comprehensive reference of current practice in the geometric design of transit facilities on streets and highways, including local buses, express buses, and bus rapid transit operating in mixed traffic, bus lanes, and high-occupancy vehicle lanes, as well as bus-only roads within street and freeway environments. It also covers streetcars and LRT running in mixed traffic and transit lanes, and within medians along arterial roadways. These guidelines are based on a review of relevant AASHTO, TRB, and ITE documents, as well as design reports provided by various transit agencies. They are designed for use by public agencies, practitioners, and developers in need of basic information about planning, locating, sizing, designing, and implementing transit facilities along roadways.

As part of the METRO Solutions program, we evaluated the impact of three Light Rail Transit (LRT) lines on traffic operations in downtown Houston. We modeled the interactions of automobile and bus traffic with three LRT lines (Red Line, East End Line, and Southeast Line). We performed traffic projections to approximate future year traffic demands, applied a trip reduction factor to account for the Downtown transit facilities, and analyzed AM and PM peak hours for future year conditions for the with interline and without interline scenarios. In the with interline scenario, the East End trains merge onto the Red Line alignment to reach the intermodal terminal while Southeast trains continue all the way to the western terminus. In the without interline scenario both East End and Southeast trains travel to the western terminus. Some of the key factors identified in this analysis to efficiently operate the LRT system include train control system, signaling coordination, effective geometric design, increasing driver awareness, effective signal timing, effective driveway control, effective signage, preemption locations, and integration between the traffic signal system and the train signal system. We recommended deploying a train control system that would modulate station dwell times as a means of continuously optimizing train headways on each of the three routes that pass through the study area. This also minimizes clustering of trains and degradation of intersection level of service. Our traffic models and analysis have served as useful tools for stakeholders to further understand the impact of the downtown LRT system.

AASHTO's bestselling publication, A Policy on Geometric Design of Highways and Streets, 6th Edition, 2011, also known as the "Green Book," is now available. This publication contains the current design research and practices for highway and street geometric design and provides guidance to highway engineers and designers who strive to make unique design solutions that meet the needs of highway users while maintaining the integrity of the environment. It is also intended as a comprehensive reference manual to assist in administrative, planning, and educational efforts pertaining to design formulation. Design guidelines are included for freeways, arterials, collectors, and local roads, in both urban and rural locations, paralleling the functional classification used in highway planning. The book is also organized into the following chapters to stress the relationship between highway design and function: Highway Functions, Design Controls and Criteria, Elements of Design, Cross-Section Elements, Local Roads and Streets, Collector Roads and Streets, Rural and Urban Arterials, Freeways, Intersections, and Grade Separations and Interchanges.