Abstract:
In Sri Lanka, rural roads are not specifically designed on technical requirements. Most
of the rural roads (C and D classes) have historical backgrounds as being tracks and
trails coming even beyond the colonial times. Hence, most of the rural roads in Sri
Lanka are almost following the same traces and not designed technically. Nowadays,
rural roads are being rehabilitated. So far those rehabilitation projects underwent with
merely construction improvements and proper geometrical improvements have not
been adopted. It was found out that the actual speeds can be significantly greater after
rehabilitation affecting the safety ofroad users. Aim ofthis study was to assess actual
operating speeds, posted speed limits and to find design operating speeds that
supposed to be after the rehabilitation. Finally it suggests rational speed limits to rural
rehabilitated roads under purview. Most of the rural roads in Sri Lanka don’t have
posted speed limits specified according to the geometric, road environment and
functionality level of the road. The speed limits of 70km/h and 50km/h are the usual
speed limits enforced for traffic in arterial roads which are categorized as class A and
B. Since the speed limits are not categorized according to the type ofthe road, above
speed limits apply to the rural roads as well. It’s hardly been seen that traffic speeds
are controlled or monitored by law enforcement in rural roads. Hence the speed
choice ofthe rural road drivers depends on variety ofother factors. The 85th percentile
speed was taken as the operating speed. This speed was used as a basis for suggesting
rational speed limit since most drivers behave in a safe and reasonable manner and do
not want to get into crashes. Also it encourages drivers to travel at about the same
speed. The researchers have studied number of rehabilitated roads in North Western
province in Sri Lanka. Each road was divided into several sections; straight and
curved. Operating speeds on straight sections were given priority in suggesting
rational speed limits. As operating speeds in curves are considerably lower and
enforcing lower posted speeds only based on operating speeds on curves for entire
road, would not be practical since drivers tend to disrespect the speed limit. The
suggested rational speed limit for all the roads under purview is 50 km/h and this
speed limit will be overridden to a lesser speed limit at a curved section based on the
operating and design speed. This speed limit should be notified using sign boards and
shall be enforced only for the curve itself.
