Highway Capacity Research on Inter-urban Highways in India
Many countries in the world have developed their own highway capacity manuals incorporating influence of local conditions on traffic flow behavior. India has also taken a giant step towards this goal. This paper presents the status of highway capacity research in India on inter-urban highways including single lane, intermediate lane, two lane and multilane highways, expressways and freeways. It gives an overview of capacity related studies during last four decades and discusses the challenges before the researchers while developing the highway capacity manual for Indian conditions, particularly due to mixed nature of traffic and non-lane based movement of vehicles on Indian highways.
Keywords Capacity. Inter-urban highway. Passenger car unit. Mixed traffic. Speed
Indian transportation system is highly skewed towards road based transportation. After the economic liberalization in the 1990s, the road infrastructure has progressed rapidly; highways are being expanded, new technology vehicles with good operational capabilities are on the roads and car own-ership has increased significantly in last two decades. The country has a total road network of around 4.689 million km giving a road density of 1.423 km per square km of land, which is much higher than that in the United States (0.65). The road network in India is classified as national highways(NH), state highways (SH), district roads and village roads, and almost two-third of the total road network is comprised of village roads, which connect villages to either district roads or to SH. Remaining one-third length is of expressways (*1200 km), NH (*92,000 km) and SH (around 180,000 km). Length of NH is less than 2 %, but it carries almost 40 % of the total traffic. SH also carry heavy to very heavy traffic. It has resulted into severe congestion on Indian highways. Government of India is spending enormous amount of money on widening of NHs from two-lane to four-lane and six-lanes. Similar efforts are being made by the state governments also on widening and strengthening of the state and district roads. Upgradation of a road is justified only when capacity of the road is related to the projected requirement of traffic. The manuals for four-laning and six-laning of highways published by the Indian Roads Congress (IRC), New Delhi have indicated certain values of design service volume for two-lane undivided and four-lane divided roads to facilitate highway development projects in the country. However, these values are ad hoc and not based on field studies. It is mainly due to very less and scattered research on the subject of highway capacity in India. The objective of this paper is to present the status of research work carried out in India on Interurban roads during last few decades. The research is compiled in three parts; undivided roads like single lane, intermediate and two-lane roads, divided roads like multilane highways, and expressways.
Research on Undivided Roads
After publication of the 1965 edition of US highway capacity manual , traffic engineers and planners in India thought of adopting capacity values as given in the manual to Indian roads also. But these were found to be unrealistic due to mixed nature of traffic and poor enforcement of traffic rules on Indian roads. Sehgal discussed the basic issues associated with Indian traffic. During 1960s, the fast moving vehicles were mainly trucks and buses and slow moving vehicles were animal or human driven vehicles. Both fast and slow moving vehicles shared the same roadway space. It was considered that HCM figure of capacity can probably be adopted if suitable passenger car units (PCU) for the different types of vehi-cles can be arrived at for Indian conditions. Therefore, capacity standards of the United States were adopted after making some ad hoc adjustments and it was suggested that capacity of a single-lane and two-lane roads in India may be taken as 420 and 1400 pcu/h respectively .These capacity values were later refuted by many researchers through their field studies[4,5] .
The first major attempt to introduce the concept of highway capacity in India was probably made in 1981 when Central Road Research Institute (CRRI), New Delhi started working on a project of road user cost study pop-ularly known as RUCS, on rural roads. Kadiyali et al.presented speed-flow relations for various categories of roads in India. They estimated capacity of a single lane, intermediate lane (5.5 m wide carriageway) and two-lane roads as 400, 1200 and 3000 pcu/h respectively. The capacity value for two-lane roads found through RUCS was much higher than that reported earlier, which was taken on judgment basis. These values were later included in IRC guidelines also. The RUCS data were updated in 1991 by collecting fresh traffic flow and speed data on roads in various parts of the country and it was found that the basic desired speeds (BDS) of vehicles have improved consid-erably during the period 1980–1990 on Indian roads. As a result, the capacity values of single lane, intermediate lane and two-lane roads were revised to 600, 1600 and 2500 pcu/h respectively.