PERCENT TIME-SPENT-FOLLOWING MODEL FOR SINGLE CARRIAGEWAY ROAD

Percent time-spent following (PTSF) is an important parameter in determining level-of-service of a single carriageway road but the current performance measure adopted in Malaysia is based on volume over capacity (v/c) ratio. Therefore, this study aims to develop a new PTSF model that is suitable for single carriageway roads in Malaysia. Traffic flow at 32 sites in various states in Malaysia were recorded using CCTV and video camera. Image processing software was used to extract volume, speed and headway data. Surrogate measure which is the percentage of vehicles travelling with headway threshold values of 3.0 and 5.0 seconds were used in estimating PTSF in the field. Initially, the base PTSF (BPTSF) model was developed and subsequently used to develop six different PTSF models using headway threshold values of 3.0 and 5.0 seconds and different variables. Analyses and performance indicators showed that the model developed based on the headway threshold value of 5.0 seconds with the inclusion of percentage of no-passing zone, opposing flow rate and percentage of heavy vehicles is the best model. This model was determined as the best fit as it has the highest score of 15, which is the maximum score based on performance indicator analysis.

Operational Considerations of Passing Zones for Two-lane Highways: Spanish Case Study

The U.S. Highway Capacity Manual (HCM 2010) methodology is used in Spain to evaluate traffic operation and quality of service. In two-lane undivided highways, the effect of limiting where drivers could pass slower vehicles, or passing restrictions, is considered through the percentage of no-passing zones. This measure does not account for how passing opportunities are distributed along the road. The objective of this research was to evaluate the effect percentage of no-passing zones and average passing zone length on a two-lane highway and, if significant, incorporate them in the analysis methodology,. The TWOPAS microsimulation program was calibrated and validated to the Spanish conditions. Passing restrictions had little effect on average traffic speed (ATS), with differences lower than 6 km/h between a road segment with no passing restrictions and a road segment with a passing restriction on 100% of its length. Conversely, passing restrictions can increase the percent time spent following (PTSF) up to 30%. Increasing the passing zone length beyond 2,000 m does not improve PTSF. The new models could be used to better estimate traffic operation on Spanish two-lane highways.

ESTIMACIÓN DEL NIVEL DE SERVICIO DE UN CARRIL LENTO

La operación vehicular en una carretera convencional depende de la atención adecuada de los adelantamientos de los vehículos lentos por parte de los más rápidos; una alternativa es mediante la provisión de carriles auxiliares a lo largo de la vía antes de pasar a una carretera multicarril.El objetivo es calibrar el modelo de simulación TWOPAS y aplicarlo en una carretera convencional española para estimar y comparar el nivel de servicio estimado en ella y en un carril lento con el resultado del procedimiento del Highway Capacity Manual - HCM.Se observó la operación vehicular en una carretera convencional de España mediante el registro a través de cámaras de control dispuestas a lo largo de la carretera, y en el carril lento, de manera que sirvió para calibrar el modelo de microsimulación TWOPAS considerando parámetros operacionales del parque automotor y aplicándolo para estimar el nivel de servicio.Se aplicó el procedimiento del HCM para estimar el nivel de servicio en segmentos de carretera con carril lento para comparar sus resultados con los obtenidos en la simulación.El modelo de simulación usado fue el TWOPAS, inserto en el Traffic Analisys Module (TAM) del Interactive Highway Safety Design Model (IHSDM), cuyos resultados en términos de Percent Time Spent Following (PTSF), Average Travel Speed (ATS) y otros permite la evaluación operacional.Los resultados y conclusiones permiten valorar la utilidad del modelo, la correspondencia de la realidad operacional en carretera y la norma española y la conveniencia operacional del carril lento estudiado.DOI: http://dx.doi.org/10.4995/CIT2016.2016.4220

Measuring Driver’s Percent-Time-Spent-Following Using a Moving Video Recording Technique

The percent time spent following (PTSF) or proportion of following time (PFT) relative to total travel time taken by vehicles to traverse a particular segment of two-lane highways has been used as key performance index for evaluating the level-of-service of the road. From the context of travel time, this implies that PTSF is a space related indicator and thus supposed to be measured over a road segment. However, this indicator is measured in the field based on specific point observation; as equivalent to the percent of vehicles traveling with time headways shorter than 3 s. The accuracy of PTSF estimates based on this approach has been questioned and criticized by many; as spot measured values may not to be real representative of segment estimates. This paper presents an exploration into the application of moving video recording technique for PTSF measurement. PTSF was estimated based on test vehicle following time on two-lane highways using moving car observer method as an alternative approach for field measurement of the indicator along road segment as opposed the existing practice of spot measurement and assumed representative of long segment. Findings from this work demonstrate that the approach used in this study is promising for field measurement of PTSF; as estimates obtained relate well with the major vehicle’s following cause factors.