The purpose of this study was to evaluate and compare the safety and operational characteristics of the single point urban interchange (SPUI) and the diamond interchange (DI) and develop guidelines that identify traffic and/or geometric conditions that favor one type of interchange over the other. State traffic engineers across the country were surveyed as to their experiences and opinions of the two types of interchanges in terms of operational performance and safety. Accident and operational data were also obtained for nine SPUIs and eight DIs. The interchange operations were studied using both field data and the computer simulation program TRAF-NETSIM. In addition, for each DI simulated, an SPUI counterpart was designed with the same geometric and traffic conditions for further comparison. No significant differences were found in the off-ramp, cross road, and overall interchange average delay. Ten volume scenarios were then developed and simulated for both interchanges at low- and high-volume conditions to analyze the effect of various traffic patterns on the relative operational performance of each interchange type. The accident data for the SPUIs and DIs were compared according to severity, collision type, and location on the interchange. No significant differences were found between the severity distribution and rates of the two interchange types. However, the proportion of on-ramp and off-ramp accidents was greater at the SPUI, and the proportion of accidents occurring in the center of the signalized intersection was greater at the DI. The proportion of angle accidents was greater at DIs than at SPUIs, whereas the proportions of rearend on-ramp, sideswipe, and fixed object accidents were greater at SPUIs. Vehicle conflicts at four interchanges in Virginia were also investigated and used along with the accident analysis results. The operational results, safety analyses, literature review, and survey of state engineers were used to develop guidelines to aid traffic engineers in the selection and design of the appropriate interchange type.

This research compares two interchange types, the Tight Urban Diamond Interchange (TUDI) and the Four Phase Single Point Urban Interchange (40SPUI). The 40SPUI is referred to in this report as a Single Point Urban Interchange with Frontage Roads (SPUI/F). The objectives of this research were to: (1) evaluate the SPUI/F based on available accident data and conflict analysis techniques, right-of-way and construction costs, and operating efficiency; (2) compare the performance of the SPUI/F and the TUDI; (3) evaluate current SPUI/F design assumptions and operation and recommend design and/or operational changes to enhance performance; and (4) evaluate the interchange form selection (pre-design) process and recommend changes where appropriate. The research found no significant difference in the safety aspects of the two interchange types. The SPUI/F generally did not perform as well operationally as the TUDI, with increased SPUI/F delay as the distance between frontage roads increased.

This guide replaces the 1984 publication entitled An Informational Guide for Roadway Lighting. It has been revised and brought up to date to reflect current practices in roadway lighting. The guide provides a general overview of lighting systems from the point of view of the transportation departments and recommends minimum levels of quality. The guide incorporates the illuminance and luminance design methods, but does not include the small target visibility (STV) method.