Degree Type


Date of Award


Degree Name

Master of Science


Civil, Construction, and Environmental Engineering


Civil Engineering

First Advisor

Peter T. Savolainen


Access management, or the management of vehicular access to adjacent land parcels, is critical to safe roadway operation, allowing state and local governments to control ingress and egress to freeways, arterials, collectors, and local roads. Access management is particularly important near signalized intersection, where nearby access points can increase the crash risks resulting from additional conflict points for vehicles traversing the primary intersection. The primary objective of this study was to examine the relationship between access point density and the frequency of crashes at signalized intersections located along state-maintained urban roadways in the state of Iowa. Information regarding adjacent access points (i.e., intersections and driveways) was collected at a total of 415 signalized intersections from 13 different municipalities. The information collected included the type of access (driveway, unsignalized intersection, alley, median opening, or field access), as well as any restrictions related to turning movements (e.g., prohibited left-turns, right-in/right-out). Access volumes were collected for public roadways and driveway volumes were estimated using trip generation models. Two subsets of crashes, total and driveway-related, were used to examine the safety-access relationship over a five-year analysis period. A series of concentric buffers were applied to investigate how the relationship between crashes and the number of access points varies spatially depending upon the buffer radius. These buffers varied from 50 ft. to 600 ft. in radius with increment of 50 ft. A series of crash prediction models were estimated to discern the impact of access spacing while controlling for other pertinent variables such as traffic volumes and roadway geometry. The results showed that the number of crashes increased consistently as the frequency of access points increased, regardless of the size of the buffer radius. However, the rate of increase in crashes tended to decrease as the buffer radius increased. The findings from this study can be used to establish thresholds for the minimum distance that an access point should be located from an adjacent signalized intersection.


Copyright Owner

Megat Usamah Bin Megat Johari



File Format


File Size

78 pages