Gravel road paving guidelines.

The percentage of gravel roads in rural areas in Kansas is higher than most states. A wide variation of traffic volumes
across different regions and variations of local conditions and scenarios present a great challenge for local agencies to determine
the suitable roadway surface type for local rural roads, especially considering constraints on transportation budgets. The primary
objective of this research was developing specific guidelines to identify the most suitable roadway surface (gravel vs. paved) for a
particular roadway section with given conditions. Surveys were carried out to determine the importance of factors affecting the
selection of a roadway surface type, which were later used for guideline development.
General guidelines were developed using the multi-criteria assessment method in order to fulfill the objectives in this
study. The key factors in decision-making in regards to paving were identified as agency cost, safety, vehicle operating cost
(VOC), traffic volume, purpose of road usage, and public preference. Multi-criteria assessment method involves calculating the
weights for the factors important in decision-making, obtaining respective scaled values for each factor for paved and gravel
surfaces, and eventually calculating the final score for paved and gravel surface type. Equations were formulated to carry out lifecycle
cost (LCC) analysis along with the present worth evaluation, which provided flexibility to calculate agency cost by
considering local conditions. VOC could be calculated for paved and gravel roads considering variations in the speeds of different
classes of vehicles, gradient and horizontal curvature of the road, and the conversion factor for cost on paved surface versus gravel
surface. Safety analysis was carried out for local rural roads in Kansas for 5 years, from 2010 to 2014, using the Kansas
Department of Transportation’s Kansas Crash Analysis and Reporting System (KCARS) database. After calculating the equivalent
property damage only (EPDO) crash rates on paved and gravel roads in Kansas, results showed that paved surfaces were in general
safer than gravel surfaces, which was taken into consideration while calculating the scaled values for safety. The final score is
calculated by multiplying the weights of each factor and their respective scaled values. The roadway surface type with a higher
score is the preferred alternative for a road section under consideration.
A computer-based Gravel Road Paving Guidelines Program was created as a user interface, using Visual Studio to carry
out all complex calculations for determining LCC and VOC considering local variations. The program also helped determine final
total scores for paved and gravel roads by considering scaled values of all important factors considered for conversion. Another
approach using cost versus traffic volume showed that the break-even point for traffic volume decreased with an increased
percentage of trucks and increased vehicle speeds. Developed guidelines help determine the best roadway surface type for any set
of local conditions. The Gravel Road Paving Guidelines Program is available upon request to KDOT#Research.Library@ks.gov.