Furthermore, a Python based program called PyNomo, has been executed with the help of several add-on packages (e.g., numpy, scipy, pyx) to generate a compound parallel scale nomograph consisting of multiple variables using the developed empirical model.

A comparative study with established methods (i.e., HCM 2016, TRRL, IRC and German method) proves the superiority of the developed model in terms of predictive capacity. For incorporating the presence of heavy vehicles in the model, all vehicle types are converted to passenger car equivalent units. Based on data collected from six roundabouts along the national highways in Bangladesh, multivariate regression method has been used to develop an empirical model as a function of entry width, rotary lane width, distance between entry and nearest exit, central island diameter, and circulating traffic flow to estimate and predict the capacity of rural highway roundabouts.

This research aims at developing an empirical model for estimating and predicting capacity of highway roundabouts considering both geometric and traffic parameters. However, presence of heavy vehicles in traffic stream lowers the overall operating speed and flow in rural highways especially at the vicinity of intersections. Transportation infrastructure plays a significant role in the economic growth of developing countries where heavy vehicles act as the backbone in transporting goods and people via highways. Some preliminary recommendations regarding speed control were generated as a conclusion of this study.

As a traffic parameter, the impact of the posted speed limit at the approach on the operational speed was also analyzed. The impact of main geometric elements – lane width, slope, and length of the straight part of the road before entrance to the roundabout was analyzed. As operational speed, v85 - speed up to which 85% of vehicles are moving was included in the analyses. The speed was measured for 24 hours at every approach. The outer radii of analyzed roundabouts were from 15 to 22 m. The experimental study presented in this paper was done on six different roundabouts, on 22 approaches, located at a regional road network. Although the approaching speed is emphasized in some research as relevant for operational speed in the roundabout, there are no detailed analyses of the effects of geometric and traffic elements on approaching speed that can be used to design safer roundabouts. Roundabouts are very often implemented as a measure for speed control at the intersections where there is a problem with traffic safety.

Sidra intersection 5.1