| The primary purpose of this research is to estimate the capability and applicability of new nano interchange designs as they compare to conventional four-level interchanges. Nano interchanges were conceived to provide drivers with high speed and short travel distances while requiring less right of way in dense urban areas where real estate is expensive. This research consists of two tasks: (1) operational evaluation and (2) safety evaluation.;The operational evaluation compares measures of effectiveness (MOEs) between nano interchanges and conventional interchanges for thirty volume scenarios comprised of varied data for through volumes, ramp volumes, and percentages of heavy vehicles. The estimations were conducted for an entire interchange and for key freeway segments.;The safety estimations were made by building safety prediction models for collisions that may occur in the influence areas of ramps. These safety models are based on negative binomial distribution and quantified safety effects of traffic, geometric, and environmental factors using three statistical methods: (1) a generalized linear model with only main effect variables, (2) a generalized linear model with main effects and interaction terms, and (3) the new Hauer method model.;The operational evaluation for an entire interchange shows that conventional interchanges perform better than nano interchanges for the volume scenarios tested. The analyses of key freeway segments show that most of operational difficulties for the nano interchanges are in diverging influence areas located on upgrade segments. The analyses also indicate that several merging influence areas that are connected to ramps with steeper and longer upgrades also have lower performance levels.;The safety prediction model developed unique linear or non-linear relationships among traffic, geometric, and environmental factors. Left-hand ramps appear to have higher collision frequencies than right-hand ramps, and on-ramps have higher collision frequencies than off-ramps.;Finally, based on these estimations, the following recommendations are made to improve the operation and safety effectiveness of the nano interchange: (1) deceleration or acceleration lanes could be extended; (2) a two-lane off-ramp or on-ramp for the nano interchange could be considered; and (3) left-hand ramps could be replaced by right-hand ramps. |
