3 Baseline Conditions
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3.1.2 Interchange and Critical Intersection Crash Experience 3 Baseline Conditions Interchanges provide an important interface between the surface street network and the Interstate This section provides a brief overview of the key baseline conditions that were analyzed to provide system. Since these access points are limited, traffic is concentrated along arterials having the proper planning framework to develop the findings and recommendations of the Plan. A more interchanges, making them more prone to congestion and crash experience. Identification of detailed analysis of each of the baseline conditions related to this study can be found in the interchanges with high incidence of crashes is important to identifying where key improvements Baseline Conditions and Needs Assessment Report, which was submitted to GDOT in February may be needed. 2007. Similar to the identification of high crash Interstate segments, comparison of interchange crash 3.1 Crash Safety and Roadway Geometrics rates to that experienced at other interchanges allows attention to be focused on those locations with the greatest need. GDOT does not calculate a statewide average interchange crash rate. Providing an Interstate system that facilitates safe movement of traffic is an important goal of Therefore, for comparative purposes, the number of crashes occurring at each interchange was GDOT. Therefore, the crash experience data from 2003-2005 were carefully examined, and compared to the average for all interchanges in Chatham County. 19 crashes per year was the conditions that could lead to potential safety problems were identified to ensure that safety countywide average based on the data from 2003 through 2005. Those interchanges with more concerns were considered in developing improvement recommendations. The latest crash crashes than the countywide average were identified. The analysis included crashes along the experience data available at the beginning of the study were used. arterial serving the interchange to a distance of one mile on each side of the interchange and all 3.1.1 Interstate/Roadway Segment Crash Experience crashes involving the interchange ramp termini intersections. The incidence of crashes along a particular stretch of road is most valuable when compared to The high crash interchanges, determined based on the above methodology, are identified in that of similar roads throughout the state. In order to make this comparison, the accident rates for Figure 3.1. As this figure shows, the following interchanges experienced crashes exceeding the the study roadways were calculated and then compared with the average rate for similar facilities threshold. It is important to note that this is a comparison of the number of crashes at each study throughout the state. The accident rate is defined as the number of crashes per million vehicle interchanges compared to the countywide average, and not a comparison of crash rates. Thus, it miles travelled (MVMT) for a given segment of roadway. For this study, crash data and statewide is possible for an interchange to experience a high number of crashes yet have a low crash rate average crash data were compared for 2003 to 2005. The following are the statewide average because of high traffic volumes. crash rates for urban and rural Interstates throughout Georgia between 2003 and 2005. • I-16 at SR 307 (# of crashes 116% of countywide average) • Urban Interstates = 195 crashes per 100 MVMT • I-516 at US 17 (# of crashes 205% of countywide average) • Rural Interstates = 78 crashes per 100 MVMT • I-95 at US 80 (# of crashes 216% of countywide average) High crash segments were identified along the Interstate system based on the criteria indicated • I-95 at SR 21 (# of crashes 258% of countywide average) above. For this analysis, the Interstate system was divided into segments comprised of an • I-16 at I-516 (# of crashes 300% of countywide average) interchange and the Interstate extending approximately halfway to the adjacent interchange. This • I-95 at SR 204 (# of crashes 321% of countywide average) resulted in I-95 being divided into six sections, I-16 being divided into eight sections, and I-516 • I-95 at I-16 (# of crashes 379% of countywide average) being divided into five sections. Figure 3.1 (see page 3-2) shows these Chatham County Interstate sections with the incidence of crashes along the Interstate sections and interchanges 3.1.3 Geometrics not Meeting Current Standards indicated. The geometric constraints along the Interstate system can be comprised of a variety of factors. Since design standards evolve over time, many of the areas that do not meet current standards The high crash segments, determined based on the above methodology, are identified in Figure were likely built according to standards at the time they were built. Current standards are taken 3.1. As this figure shows, the only Interstate segment to surpass the urban threshold is along I- from the most recent (2004) available American Association of State Highway and Transportation 516 east of the southwest bypass to its easternmost terminus at Montgomery Street. Sections Officials (AASHTO) “Green Book.” surpassing the rural threshold include: For example, curvature of the current Interstate could be too sharp to accommodate current • I-95 from the Bryan County Line to Quacco Road motorist speeds, the ramp length or curvature may not satisfy current GDOT standards, or bridge • I-95 from south of SR 21 to the South Carolina State Line load sufficiency may not match projected traffic characteristics. 3-1 Figure 3.1: Crash Experience Along Freeway Segments and at Interchanges 3-2 The bridge sufficiency rating is an evaluation of a bridges’ ability to stay in service. A bridge’s weaving distance from the Gwinnett Street ramps to the I-16 ramps needs to be 2,000 feet, per sufficiency is rated from 0 to 100, with 100 representing a fully sufficient bridge and 0 representing current standards; the existing distance is 500 feet. an entirely deficient bridge. Bridges must have sufficiency ratings of 50 or below to be eligible for federal replacement funds. As Figure 3.2 (see page 3-3) indicates, none of the Interstate bridges were identified as having a sufficiency rating below 50. 3.2 Truck Traffic Characteristics The truck traffic analysis estimated the present and future truck traffic volume and routes taken Numerous locations were identified as having potential roadway geometric concerns. The from industrial sites, warehouse and distribution facilities, trucking companies and the seaports to locations evaluated are indicated on Figure 3.2 and listed below. The investigation focused on the Interstate system in Chatham County. The analysis was conducted through a series of the following: interviews and surveys, field research, and GIS was employed to identify existing and forecasted • Curvature of ramps truck traffic activity in Chatham County. The analysis was conducted in close coordination with • Length of ramps the State Truck Lane Study and the SRTA Northwest Toll Expressway Study. • Length of merge lanes (weaving space) • Overall roadway alignment and its curves 3.2.1 Truck Generators A list of industrial sites in Chatham County was obtained from the Georgia Department of Industry, 3.1.3.1 I-16 at I-95 Interchange Tourism and Trade (GDITT), now the Georgia Department of Economic Development (GDED). The full cloverleaf design results in short weaving areas along both Interstates. These weaving Independent research was completed as well to identify and include warehouse and distribution areas currently accommodate peak hour weaving volumes greater than 1,000 vehicles along both facilities and trucking companies in the Chatham County area. Altogether, 130 facilities meeting Interstates (I-95 southbound and I-16 westbound weaving areas). These volumes are expected to the specified criteria were identified. grow significantly by year 2030, further worsening the operational deficiencies created by these weaving segments. A questionnaire/survey form was developed in an attempt to solicit the necessary information from the identified sites. Questions asked included; 3.1.3.2 I-16 at I-516 Interchange This partial cloverleaf design uses directional ramps to serve I-516 southbound to I-16 eastbound • How many trucks go in and out of your facility per day? and I-516 northbound to I-16 westbound movements. This removes the short weaving section • What roads do the trucks take to reach the Interstate system from your facility? created with the full cloverleaf interchange, but requires a left-side entry and merge for traffic • What type of trucking is most prevalent at your facility (long-haul, short-haul, local or traveling from I-516. Additionally, the loop ramps have a 25-mph design speed; the curve radius transfer)? is 200 feet. • What roads do the trucks try to avoid? • What road or intersection in your area is most in need of attention? 3.1.3.3 I-16 from Chatham Parkway to Downtown Many of the shoulders and bridge widths do not meet current standards. The eastbound curve Attempts to contact all 130 facilities were made. Usable information and results were returned by th turning north at the 37 Street connector has less than a 1,800-foot radius needed for 70 mph 79 facilities. From their feedback, it was determined that these 79 facilities generate 3,553 trucks design speed. The exit ramp to US 17 northbound is too short. In addition, the last eastbound per day. According to the responses of the trucking companies and facilities responses, trucks exit ramp’s taper is too short. most often use SR 21, Jimmy DeLoach Parkway, SR 307 and US 80 to get to the Interstate system. Although this is not a comprehensive total, this information gives a good basis for 3.1.3.4 I-516 assessing the truck traffic and volume on the roadways in Chatham County. I-516 was originally designed as a local freeway facility and not an Interstate.