Presentation | 2013

Access Management Sight Distance Applications

Overview • Review of Sight Distance Components • Common Sight Distance Applications to Access Management • Sight Distance – What, When, and Where • Concluding Remarks Slide Titles Another Look at Sight Distance Applications for Access Management Overview Sight Distance Review of Candidate Sight Distances Basic SSD Assumptions Review of Candidate Sight Distances Basic DSD Assumptions Review of Candidate Sight Distances Common Applications That Consider Sight Distance for Access Management Looking at Stopping & Decision Sight Distance Assumptions Basic Questions Stopping Sight Distance for Different PRT Values Stopping Sight Distance for Different PRT & A Values Decision Sight Distance and Stopping Sight Distances Decision and Stopping Sight Distances (varying PRT and A values) Concluding Thoughts • Sight Distance Assumptions dramatically vary based on supporting assumptions • Extreme values for sight distance and it’s application to unsignalized access spacing, median openings, and corner clearance may create impractical recommendations • Access Management applications may warrant unique considerations such as: ? Use unique PRT values for Access Management ? Consider if casual, urgent, or some other deceleration values are appropriate ? Assess the best speed to use for these assessments Final Thoughts • Based on their definitions, Decision Sight Distance seems to be more appropriate to access management spacing considerations but… ? A road with more than one lane in each direction may need to be evaluated in a different manner than those with only one lane in each direction (since lane changes are possible) ? When assessing access spacing, at what point does a driver quit focusing on the closest driveway and begin to focus on a downstream driveway? Should this shift in driver attention be more directly considered when developing spacing standards?

Driveways, Effects
Sight Distance, standards