"In general, the public more easily accepts the lack of flexibility in motorway design because of the purpose of these roads, mobility is gained at the expense of aesthetic treatment. Greater design flexibility was observed for urban and rural non-motorways that are typically responsive to site-specific conditions."

DESIGN FLEXIBILITY

All countries visited utilize design guidelines for roadway design that are considered central to their design philosophy. These guidelines are typically more strict for motorways and are applied more as standards and with greater conformity to these roads. All countries visited have a design exception process through which to address departures from design guidelines. This process is more frequently applied to non-motorways. It was also noted that, in general, the public more easily accepts the lack of flexibility in motorway design because of the purpose of these roads — mobility is gained at the expense of aesthetic treatment. Greater design flexibility was observed for urban and rural non-motorways that typically are responsive to site-specific limitations. Thus, the wider acceptability of such design departures may be due to the fact that each problem area is addressed within its context and constraints.

Commitment to creating a roadway environment that addresses safety, capacity, economic, and environmental concerns has also shaped the wider acceptance of design flexibility. The British Design Manual has a section for such deviations in each roadway component that discusses possible reasons for deviating (relaxing) the suggested guidelines. This approach reinforces the concept of adjusting the roadway design to the specific local requirements. It should be noted that although the Manual emphasizes the use of appropriate design and implementation of desirable values, at the same time it arms the designer with possible flexibility.

All these countries have or are currently revising their design guidelines. This process may have made them more aware of the need to view their design guidelines as a flexible tool for those designs where human and environmental needs may play a stronger role in shaping the final roadway design. In addition, realizing the possible limitations of the previous guidelines may have significantly impacted current acceptance of such flexibility, since the new guidelines are now geared to address road purpose and to create a uniform look for each road category. The experience of developing new guidelines has allowed these agencies to understand the value of design flexibility and exceptions.

Set documentation, which was very extensive in England, is required to justify departures from the design guidelines. Moreover, the Highways Agency in England has a manual that describes how and when design departures are to be requested and identifies the types of documentation needed to support such a request. In a typical project, the designer has to visualize the project and determine how to approach it. Then, each departure needs to be justified and explained to the Safety Office of the Agency, which has ultimate decision authority. Several components of the project are set, similar to the AASHTO minimum criteria, and these components require official documentation. Designers have the latitude to alter other, more minor components at their discretion to address the specific needs of the project. In general, the countries are shielded from legal liability regarding design defects. The exception is England where litigation is expanding regarding departure from design guidelines; most of the litigation is settled out of court.

In the countries visited, the guidelines issued by the national highway authorities are usually considered as recommendations for any projects under the authority of local governmental agencies. This provides great flexibility in designing to meet the local needs and conditions.