This study explores the effects of bypass roads on the build form of small towns in Sri Lanka. The small towns analysed are Avissawella, Mawanella, Balangoda and Piliyandala.The results of the study indicate three impact scenarios: i) the bypass road has more accessibility than the existing main road and new land uses, and high-density areas emerge along the by-pass road, making this the town centre; ii) both bypass road and the existing main road show similar levels of accessibility and attractiveness. iii) accessibility of the existing main road remains higher than the bypass road and very new developments are attracted towards the bypass road -thus the existing main road remains the main centre of the town. The results confirm that spatial and economic forces are closely interrelated as indicated in the theory of the natural movement economic process. However, the study found that the above forces are constrained by natural barriers. These findings are useful for transport engineers when making new strategies to implement bypass roads and to urban planners to develop local development plans after constructing bypass roads.