This section provides an overview of CSS. What it is and how it can help to shape transportation projects around the country. Feel free to browse through the topics below or search for a particular page by entering a keyword in the search box below or clicking on "Advanced Search."
Intersections present challenges in any transportation project. With CSS, innovative techniques and tools are being developed to address this important aspect of road design. These techniques help make streets and roads safer and easier to cross, and reduce accidents and conflicts. In cities and towns, intersections can become lively street corner environments.
Article / Paper / Report
Real Intersection Design: Leaving Theory Behind for Design
The Real Intersection Design (RID) concept was born out of
frustration with the usual conference fare. Often, presentations
and sessions deal with only the theoretical, and many in the
audience never emerge from their rhetorical shells (witness the
post-session talk at controversial sessions). While plans and
guidelines play an important role in the formulation and
development of our transportation system, discussions of the
application of that knowledge are often scant.
An example is the case of the free turn lane. Is the convenience
for drivers and cyclists worth the inconvenience to walkers,
especially those with limited vision? Do the additional crossings
help or hinder pedestrian flow? How does one weigh the impacts
to land use and access? Yet no intersection is an island, and
each design is site specific. In fact, most streets and intersections
in the built environment are site specific, and it takes actual design - not abstract rhetoric to make each work.
The RID concept has three objectives:
1. To get participants - often people with vast amounts of
knowledge - out into the field where they can give
something back to the community.
2. To foster intense interaction between experts and lay
people.
3. To test the theory that site conditions often permit just a
few alternatives, a priori solutions, and each can usually be
made to work for most users. The question is balance and
understanding the requirements of each user group.
-- Michael King et al.
Excerpt
Intersection Sight Distance (ISD): Flexibility in the AASHTO Guidelines Provision for sufficient ISD is recognized in the AASHTO Green Book (2) as important for overall intersection operations. For unstopped approaches, the Green Book (2) notes that the provision of SSD will generally provide sufficient distance for drivers to perceive conflicts. Intersection sight distances that exceed stopping sight distances for unstopped vehicles "enhance traffic operations." more...
from
A Guide for Achieving Flexibility in Highway Design
Excerpt
Intersection Sight Distance (ISD): Mitigating Limited Intersection Sight Distance Where limited ISD exists according to the AASHTO Green Book (2), the designer has a number of options depending on the nature of the sight restriction. Every attempt should be made to eliminate sight restrictions such as trees, vegetation, signs, and movable obstacles. Where such obstacles cannot be moved, field investigations can determine whether the driver can safely position the vehicle such that actual sight lines (versus those specified in the design model) are clear. more...
from
A Guide for Achieving Flexibility in Highway Design
Article / Paper / Report
Pedestrian Safety through a Raised Median and Redesigned Intersections
Documentation was done on the effect of a raised median, signalized and redesigned intersections, curbs, and sidewalks on vehicle speed, pedestrian exposure risk, driver predictability, and vehicle volume along a four-lane suburban roadway in central New Jersey. The results are that the 85th-percentile vehicle speed fell by 2 mi/h and pedestrian exposure risk decreased by 28 percent. Also, the median allows pedestrians to cross one direction of traffic at a time and signals, curbs, median, redesigned intersections, and striping patterns work together to manage driver behavior. In regard to vehicles, it was found that vehicle volumes were not affected and that vehicle speeds acted independently of vehicle volumes. A collision analysis projected a savings of $1.7 million over the next three years in direct and indirect costs. The goal of the report was to produce a simple and straightforward analysis tool for similar projects in the area.
from
A Guide for Achieving Flexibility in Highway Design
Excerpt
Intersections: Mitigating Nontraditional Intersection Design Treatments Designers may occasionally be constrained with respect to the lane arrangements, geometry, or design vehicle that can be accommodated. Mitigation efforts may include placing roadside objects (lights, sign poles, signals, etc.) farther from the edge of pavement so large vehicles do not collide with them. The use of mountable or painted end treatments on raised barriers provides more room for encroachments. more...
from
A Guide for Achieving Flexibility in Highway Design
