Highway Capacity Manual (HCM) assumes that traffic flow rates are equally distributed between lanes, which is not always the case. Lane distribution and speed are influenced by lateral clearance on the roadsides. In Jordan, the absence of well-marked lanes and poor lane discipline results in under-utilizing of the freeway capacity. The objective of this study is to look into the impact of the presence of roadside objects on lane distribution and speed. Test sections were selected on six-lane freeway segments located in sub-urban areas on tangent highway segments. Speed measurements and distribution counts made for each lane on a directional three-lane segment of the freeway. The results showed that lane distribution significantly varies depending on lateral clearance and traffic. As lateral displacement increases, right-lane-use and left-lane-use increases while the middle-lane use remains almost at the same level. Average speed increases as the lateral clearance increases. The results also showed that average speed and lane distribution for 1.5m lateral clearances are very similar to no obstacle conditions. The impact of an obstacle is more significant on the right lane while the use of the left lane fluctuates with a significant increase if traffic flow rates reach high levels.

Critical gap and follow-up times are two important fundamental traffic parameters used in the design and operational analysis of roundabouts and un-signalized intersections. Moreover, they are used to assess capacity and level of service at minor roads. In Jordan, roundabouts are used extensively, and therefore, there is a need to conduct studies on follow-up and critical gap time. The driver behaviour in Jordan can be described as aggressive in terms of their choice of follow-up headway at roundabouts. In this study, the roundabouts were located in mountainous terrain which allowed the collection of critical gap observations for approach slopes ranging from 6% up to 8%. The critical gap and follow-up times were recorded and analyzed. This research also identified other factors affecting critical gap, lag and follow-up times such as geometry of roundabout, slope of the approach, culture and behaviour of drivers. This research also proposes a significant relationship between approach slope at roundabouts and the observed gap. This relationship may be incorporated in the estimation of capacity and level of service determination at roundabouts. The results of this study should assist highway and traffic designers in the design and the performance evaluation of roundabouts.

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