A Case Study: The 85th Percentile Operational Speed of a Two-Lane Rural Highway at Different Road Segments for Different Speed Limit Signage Colours

Nur Zalikha Abdul Jalil; Muhammad Akram Adnan; Norliana Sulaiman

Authors

Nur Zalikha Abdul Jalil Department of Civil Engineering and Drainage, Kuala Lumpur City Hall, Jalan Raja Laut, Kuala Lumpur, Malaysia
Muhammad Akram Adnan School of Civil Engineering, College of Engineering, Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia
Norliana Sulaiman School of Civil Engineering, College of Engineering, Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia

Keywords:

85th percentile, operating speed model, horizontal curve, traffic volume, speed limit, coloured signage

Abstract

A study has been conducted to evaluate the safe operational speed at the 85th percentile. It was aimed to provide the best signage colour that is visible to alert road users. It is very important to facilitate the road with a clear signage to allow road users to be more aware of the necessity to obey to the speed limit. This can avoid unwanted incidents from happening at the most crucial part of the case study which is at the mid-curve. The speed data was collected from a two-lane rural highway along the horizontal curve of Jalan Bukit Palong Lukut, Port Dickson, Negeri Sembilan. The road is classified as Federal Route 5 (FR5) and Rural 5 (R5) at a flat terrain with 90km/h design speed. The 85th percentile was obtained based on four (4) conditions starting with the absence of any signage followed by the installation of yellow signage, red signage and white signage. The varying-coloured speed limit signage is posted before approaching the tangent line in a staggered manner for a safe and smooth manoeuvring before entering the curve section. The traffic volume was gathered simultaneously using the tally counter for the northbound direction and southbound direction. Two sets of data were collected during the day and nighttime respectively for both traffic counts and spot speed data. Road configurations were measured using the measuring wheel. Several analyses have been carried out using the Minitab® Statistical Software to generate results like the regression analysis and paired t-test. It was observed that during the day, the data was more significant since traffic was heavier, and vehicles could not drive at a higher speed than the speed limit whereas vehicles tended to speed up during night time due to the lesser number of vehicles causing the results to be insignificant. The findings obtained from this study should be beneficial for practitioners in deciding the best colour selection for a speed limit signage and its effectiveness.