27 CAR § 95-505. Identify safety considerations in design alternatives

(a)(1) Once the safety analysis is complete in the purpose and need, safety issues and considerations in the evaluation of conceptual design alternatives should be identified. (2) The IJR should demonstrate that the proposed alternatives will not have significant or adverse impact on the safe operation of the freeway system. (3) The IJR should also identify any design features that may result in a higher risk of safety impacts. (4) Figure 6 shows a table of safety impacts of not implementing certain design features. (b)(1) Some safety impacts of alternatives are highly dependent on traffic forecasts, such as inadequate turn lane storage or inadequate weaving length. (2) It is therefore crucial that a sensitivity analysis, as outlined in 27 CAR § 95-401 et seq., should be considered to determine the risk of such impacts. (3) Conflict areas with significant traffic volumes on the crossroad (such as busy driveways near the ramp terminal intersection) or on the freeway main lanes (such as closely spaced ramps), particularly that can result in a high speed differential, should be identified and considered in the analysis. Geometric Feature Operational Effect Safety Impact Lack of route continuity Excessive lane changing Violate driver expectations Increased signing requirements Moderate No lane continuity (basic lanes) Excessive lane changing Moderate No lane balance (exit entrances) Increased lane changing Moderate Inadequate application of auxiliary lanes Capacity reduction Increased lane changing Moderate Left exits/entrances Increased lane changing Two-sided weaving (across all lanes) Increased signing requirements High Two exits/interchanges Increased signing requirements Potential driver confusion Moderate Exit beyond crossroad Reduce exit visibility Driver comfort/convenience Moderate Inadequate exit/entrance design Short taper/parallel Small radius at exit/entrance gore Inadequate merge/diverge opportunities Inadequate speed for entering vehicles Exiting vehicles slow on main lanes-speed differential Moderate Inadequate exit ramp length Queuing onto main lanes High Inadequate weaving sections Short weaving section Two-sided weaving section Capacity reduction Excessive lane changing Lane changing across all lanes Speed differential between vehicles-all lanes High Inadequate decision sight distance Driver confusion/indecision Driver comfort/convenience Moderate Source: Freeway and Interchange Geometric Design Handbook, 2005, ITE Figure 6. Freeway and Interchange Geometric Features Impacting Operations and Safety (c)(1) Other safety impacts of alternatives are highly dependent on geometric design, such as the use of a low-speed exit loop ramp that may meet geometric standards but may not be consistent with driver expectations. (2) Any design exceptions for any alternative that may have a safety impact should be identified in the IJR. (d)(1) Currently, there is little in the way of widely accepted safety guidance and tools available for agencies to use in the analysis of safety performance of highways. (2) As a result, safety considerations often carry little weight in the project development process. (3) However, with continued emphasis being placed on reducing the numbers of fatal and serious crashes on the highway system, new approaches and tools for the quantitative analysis of safety performance are being developed. (4) For instance, two (2) new tools for the analysis of safety performance that will have a large impact on the development of highway projects will be the Highway Safety Manual and the Interchange Safety Analysis Tool. (5) The Federal Highway Administration Interstate System Access Informational Guide provides additional guidance regarding safety analyses that may be appropriate in an IJR.