Road narrowing is a part of the road with the condition of traffic capacity after that (down stream) is smaller than the entrance (up stream). Road with conditions like this can occur for example when entering the bridge, the occurrence of an accident that cause a part of the road width is closed. In the event of a road repair or other condition, resulting in a change in vehicle travel from the free flow (uninterrupted flow) become distracted (interrupted flow) so that there is a decrease in speed and increased density between vehicles. On the Pancasan highway, there is narrowing of the road located in Ajibarang kulon village, Ajibarang district, Banyumas regency, which is quite significant density. Therefore, there needs to research on the characteristic of traffic flows using the Greenshild method and service levels reviewed from the speed of light vehicles. An acquired mathematical relationship between speed to density on the road does not narrowly get result 10.49 km/h as for the narrow road 6.89 km/h with a difference of 20.71 %. For a mathematical relationship between volumes to the density of the road does not narrow the result of 44197 vehicles/hour as for the road narrowed 492.07 vehicles/hour with difference of 5.36 %. For a mathematical relationship between the volumes to the speed on the road does not narrow the result of 1067.21 vehicles/hour as for the road narrowed 1179.77 vehicles/hour with 5 % of the contents. On the Pancasan highway, there is a decline in service levels, from the normal wide road to the narrowing i.e. from the service level D (37.88 km/h) to the service level F (26.43 km/h).