Ida van Schalkwyk

Evaluation of the Scottsdale Loop 101 automated speed enforcement demonstration program

Speeding is recognized as a major contributing factor in traffic crashes. In order to reduce speed-related crashes, the city of Scottsdale, Arizona implemented the first fixed-camera photo speed enforcement program (SEP) on a limited access freeway in the US. The 9-month demonstration program spanning from January 2006 to October 2006 was implemented on a 6.5 mile urban freeway segment of Arizona State Route 101 running through Scottsdale. This paper presents the results of a comprehensive analysis of the impact of the SEP on speeding behavior, crashes, and the economic impact of crashes. The impact on speeding behavior was estimated using generalized least square estimation, in which the observed speeds and the speeding frequencies during the program period were compared to those during other periods. The impact of the SEP on crashes was estimated using 3 evaluation methods: a before-and-after (BA) analysis using a comparison group, a BA analysis with traffic flow correction, and an empirical Bayes BA analysis with time-variant safety. The analysis results reveal that speeding detection frequencies (speeds> or =76 mph) increased by a factor of 10.5 after the SEP was (temporarily) terminated. Average speeds in the enforcement zone were reduced by about 9 mph when the SEP was implemented, after accounting for the influence of traffic flow. All crash types were reduced except rear-end crashes, although the estimated magnitude of impact varies across estimation methods (and their corresponding assumptions). When considering Arizona-specific crash related injury costs, the SEP is estimated to yield about

Differences in the Performance of Safety Performance Functions Estimated for Total Crash Count and for Crash Count by Crash Type

17 million in annual safety benefits.

Influence of Land Use and Driveway Placement on Safety Performance of Arterial Highways

In recent years the development and use of crash prediction models for roadway safety analyses have received substantial attention. These models, also known as safety performance functions (SPFs), relate the expected crash frequency of roadway elements (intersections, road segments, on-ramps) to traffic volumes and other geometric and operational characteristics. A commonly practiced approach for applying intersection SPFs is to assume that crash types occur in fixed proportions (e.g., rear-end crashes make up 20% of crashes, angle crashes 35%, and so forth) and then apply these fixed proportions to crash totals to estimate crash frequencies by type. As demonstrated in this paper, such a practice makes questionable assumptions and results in considerable error in estimating crash proportions. Through the use of rudimentary SPFs based solely on the annual average daily traffic (AADT) of major and minor roads, the homogeneity-in-proportions assumption is shown not to hold across AADT, because crash proportions vary as a function of both major and minor road AADT. For example, with minor road AADT of 400 vehicles per day, the proportion of intersecting-direction crashes decreases from about 50% with 2,000 major road AADT to about 15% with 82,000 AADT. Same-direction crashes increase from about 15% to 55% for the same comparison. The homogeneity-in-proportions assumption should be abandoned, and crash type models should be used to predict crash frequency by crash type. SPFs that use additional geometric variables would only exacerbate the problem quantified here. Comparison of models for different crash types using additional geometric variables remains the subject of future research.

Balancing Urban Driveway Design Demands Based on Stopping Sight Distance

Characterizing driveway safety is a relevant and relatively complex topic in transportation safety research. This research studied the safety link of driveways abutting Oregon highways and considered various factors proposed in the current literature for design and evaluation of the safety performance of roadside elements. On the basis of two probability samples from rural and urban arterial state highways, this research developed alternative safety performance functions to evaluate the safety impacts of various driveway configurations. These safety performance functions were intended to explore driveway safety beyond the average driveway density treatment commonly encountered in the literature. The statistical models and methodologies in this research are comparable with those in the Highway Safety Manual. The proposed models exhibited different ranges of effects for urban and rural conditions, but type of land use proved a prominent factor for both the urban and the rural models. The analysis showed that roadside safety is influenced mainly by driveways associated with commercial and industrial land uses in the urban environment. Similarly, industrial driveways are more influential for safety than other types in rural environments. In addition, the rural model uncovered a safety connection to clusters of driveways rather than to driveways alone. This research indicated that after driveway land use in rural environments was accounted for, clustered driveways tended to have fewer crashes compared with isolated driveways.

Highway Safety Manual Training Materials

Many roadways in urban areas, especially dense commercial areas, are subjected to on-street and adjacent off-street parking demands; local access through driveways is an essential component of these complex urban corridors. Vehicles entering and exiting these driveways–-and their interaction with parked cars, other moving motorized vehicles, bicycles, and pedestrians–-present challenges for a safe and efficient roadway corridor. The location and the design of these driveways, together with parking and bicycle facilities, generate sight distance challenges that affect pedestrians and bicyclists. This paper investigates the type and nature of impacts–-including conflicts, sight distance, operations, and safety at driveway locations–-as they relate to pedestrians, bicyclists, and drivers. It also analyzes design geometrics that may help to provide adequate sight distance for safety at driveways with and without bicycle lanes present. Parked vehicles often obstruct drivers’ view of approaching motor vehicles and bicycles. In many locations, vehicles exiting driveways must edge out into the active travel way for the driver to have an unobstructed view. Driveway location and design analysis demonstrate the value of bicycle lanes in providing enhanced sight distance. Current practices permit longitudinal placement of on-street parking too close to driveways. For safety reasons, agencies should consider excluding on-street parking on roads with bicycle lanes when speeds exceed 30 mph so as to provide adequate sight distance without creating sporadic on-street parking spacing. Roads without bicycle lanes often do not provide adequate stopping sight distance at on-street parking driveway locations when motor vehicle operating speeds exceed 25 mph.

Incorporating Safety into Long-Range Transportation Planning

This report provides the training materials to aid in implementing the AASHTO Highway Safety Manual (HSM). The training materials provide a broad overview of the HSM format and procedures. The enclosed CD-ROM (CRP-CD-106) includes presentation slides with speaker notes, participant handouts, interactive sample problems, smart spreadsheets, and similar supporting documents. Since the target audience for this training is transportation professionals who are not required to have a vast knowledge of safety assessment procedures, the collection of training material includes basic introductory information as well as specific content for advanced procedures where appropriate. The report also briefly addresses the preferred expertise of the candidate instructors so as to enhance the learning experience for all involved parties. The report will be of particular interest to safety practitioners responsible for developing and managing highway safety improvement programs.