International Journal of Engineering Science and Computing, April 2016 3886 http://ijesc.org/ DOI 10.4010/2016.899 ISSN 2321 3361 © 2016 IJESC Impact of Horizontal Alignment on Traffic Flow Characteristics of National Highway NH-76 Tiza Michael 1 , Bhavesh Joshi 2 PG Scholar 1 , Ph.D Scholar 2 Aff.m ASCE, Career Point University, India 1 , CE, CTAE, Udaipur, India 2 Abstract: Two-lane, two-way highway facilities represent the majority of the total length of highway network in many countries. The geometric design of such facilities is considered as one of the most important factors affecting the traffic performance and safety issues, especially the horizontal alignment. However, the interaction between the horizontal curve design elements and the traffic performance still unclear and needs more investigations. This paper aims to explore the relationship between the characteristics of horizontal alignment and the traffic performance. The follower density, a new and promising performance measure, is herein used as a measure of effectiveness (MOE), since the currently used MOE (in HCM-2000), percent-time-spent-following (PTSF), is hardly observed in the field. In this study, the traffic data are collected from mid-tangent and mid-curve points at nine different sites with various horizontal alignment characteristics. Then, several relationships between the follower density, flow rate, horizontal alignment characteristics (curve radius, tangent length), and average speed are investigated. The results shows that the horizontal alignment characteristics have a significant effect on the follower density, especially curve radius value, by decreasing radius, the follower density increases (i.e., traffic performance decreases). It is also noticed that a value of horizontal curve radius falling between 400 and 450m seems to be a threshold of the significant impact of curve radius on traffic performance. It is worth to mention that the results and relationships presented in this paper is a step towards understanding the interaction between horizontal alignment and traffic performance at two-lane highway facilities and more investigation at other locations and under different traffic conditions are recommended. Key words: T.C, SSD, OSD, C.V, HCM, TRB etc. 1. INTRODUCTION Four-lane, two-way highways present a particular challenge to highway engineers as they constitute the majority of any network in terms of distance (kilometers), .Measuring traffic performance at these facilities is a complex issue due to their unique characteristics, since a single lane is provided for travel in each direction resulting in higher level of interaction between vehicles traveling not only in the same but also in opposing directions. Thus, attaining a desired speed movement in the Four-lane highways traffic stream is dependent on the ability to pass slower vehicles ahead, which in turn is a function of oncoming traffic level and geometry characteristics. The interaction between the geometric design and traffic performance at four-lane highway facilities are still unclear and needs more investigations. Understanding how the horizontal alignment parameters affect the operational characteristics of traffic on two-lane highways could be very useful for highway practitioners. This paper aims to investigate the interaction between the traffic performance and horizontal alignment at rural four- lane highways. The follower density (number of follower vehicles per a kilometer) is used as a measure of performance in this study. Recently, the follower density is proved to be a useful measure of performance at four-lane highways in several studies. On the other hand, the horizontal alignment is investigated in terms of tangent length and curve radius. The relationships between the follower density and the horizontal curve parameters, as well as between the follower density and average speeds at the mid-tangent and mid-curve points over 9 different sites are carried out. 2. LITERATURE SURVEY Varieties of research studies were reviewed to help identify issues which are related to the vehicle speed at horizontal curves, through available methods and by considering some factors in such a manner that should be analyzed in horizontal curves, literature review was not limited to, but did include on emphasis on vehicle speed models associated with horizontal curves, vehicle speed data collection & linear mixed model. A traffic study is conducted to evaluate the transportation system serving an area and to identify any improvements necessary to accommodate existing or projected traffic volumes. The study consist of data collection, including existing traffic volumes and turning movements counts, projected traffic volumes, and the identification of required movements such as traffic calming volumes. Any identified may include a feasibility analysis, include identification of impacted properties, impacted structures, alternate alignments, physical constrains and roadway design criteria to be used. Highway Capacity Manual Concept for Evaluating Traffic Performance of four- Lane Highways:- The Highway Capacity Manual (HCM) published by the Transportation Research Board (TRB) presents the widely accepted standards for analysis of two-lane highway capacity and quality of service. The first edition of the HCM was Research Article Volume 6 Issue No. 4