2001-03-19 Special Called Regular Meeting and Public Hearing

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'I' '~ e e @ f ~< Achieving Traffic Safety in Residential Subdivision Design 87 ., Lane widths must be selected with judgment. If heavy truck traffic is anticipated, an additional one foot in width is desirable. All the lane-width requirements and inter- section design controls should be evaluated when making the lane-width selection. For instance, a wider right-hand lane that provides right turns without adjacent lane encroach- ment may require a narrower left-turn lane. Local practice and experience regarding lane widths should also be evaluated. Special lane widths for such instances as bike lanes within the roadway require special attention. At arterial speeds there is substantial danger that a driver will lose control of the vehicle if the curb is struck. Therefore, the gutter should not be considered as part of the traffic lane on arterial streets. Nor should it be considered as part of the traffic lane on major collectors in areas of commercial use or in other locations where high volumes might be expected. ACHIEVING TRAFFIC SAFETY IN RESIDENTIAL SUBDIVISION DESIGN Two characteristics distinguish a residential subdivision designed with traffic safety in mind: H-.;Lj+P s~?-. 1>1,{,<<- JA- ,L orl() ~~ ~ ~ert-V\f\L.. '5!'fflEe:r~, 2. ... . ... b ~ .D \ {:\ Y\ r\IO~ There are a limited number of access points with the major arterial streets which border the subdivision. These access points are the major collectors serving the subdivision and are commonly spaced at intervals of at least one-quarter mile. The internal street system is discontinuous so as to discourage through traffic from penetrating the subdivision, 77.7 Limited Gridiron , access Figure 4-3 Average number of accidents per year. SOURCE: Harold Marks [19]. These characteristics also make a residential area a more desirable place to live, which preserves property values and helps to stabilize land uses. Marks [19,20] has demonstrated the superiority of this design, which, in view of the first characteristic given above, has become known as the limited-access division. As indicated in Figure 4-3. the gridiron subdivisions experience nearly eight times the number of accidents as limited-access subdivisions (77.2 as compared to 10.2). The superiority of the limited-access subdivision is further demonstrated by Figure 4-4. Fifty percent of the intersections in the gridiron subdivisions experienced one or more accidents in the five- year period compar~~ to less than lO9'e in the limited-access subdivisions. Marks also found three-way intersections within the subdivisions to be much safer than four-way intersections. As shown in Figure 4-5. the likelihood of an accident at a three-way intersection is. less than 10% per year. Four-way intersections were found to have an accident expectancy of over 27% in limited-access subdivisions and about 56% in gridiron subdivisions. These data clearly show that superior traffic safety of the three-way configuration for all intersections within a residential subdivision. The four-way intersection should not be used except where traffic movements on two of the approaches result in the inter- section's functioning ,as "opposing three-way intersections" (see Figure 4-6). Jog inter- . , .. L 56% 2.8% Figure 4-4 Percent of intersections having one or more accidents in a five-year period. SOURCE: Harold Marks [19]. ~",., Limited Gridiron access 3-way 4-way