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Abstract
Finding a best rout between two points of a network is a common task in most Geographic Information Systems (GIS). A network and its segments are normally evaluated based on the distance or time required to travel from one node into another. The best path is, then, defined such that the total time or distance between the two nodes is at a minimum. Unfortunately, within road networks using time or distance alone may lead to results not necessarily desired by users. Thus, a number of additional factors which maybe somehow compulsory, need to be taken into account. In other words, a user may additionally be interested to choose his/her rout based the amount of road traffic, climate, road width and class, nearness to tourist or religious centers, hospitals, and petrol stations and so on. As a result, parameters of such may need to be taken into account in order to obtain more realistic and satisfactory decisions in a road network analysis. This paper is concerned with the development of a suitable cost model, derived based on a number of quantitative and qualitative parameters which affect the value of a road segment. Once formed, the model was tested in parts of Iran road network. Due to the diversity of weather conditions and user tastes the model was implemented and evaluated in four separate cases. The preliminary results showed that utilising the parameters presented in this article and the way they are formulated, can lead to routs of more satisfaction to users.

1- Introduction
In Geographic Information Systems (GIS), network analysis is one of the most powerful tools. Selecting optimum paths for inter-cities traveling, transportation vehicles of domestic, directing the bus fleet of tourism corporations and international transportation companies are some examples of network analysis applications. So different parts of the routes network are evaluated considering their distance and required time to pas each part to analyze the optimum route to take. Unfortunately the route analysis through these two variables of time and distance can determine the exact specifications of network and practically results in dissatisfaction of GIS users. In next sections of this paper it will be shown that considering sufficient and suitable variables in selecting routes based on GIS environment will results in better suggestions about the optimum route between Tehran and Mashhad following section introduces the proper effective criteria used in cost model.

2- The Criteria in roads cost
Basically the main criteria effecting on roads are divided in to three groups of road humane and vehicle factors [Sadeghi –2002]the road criteria include that kinds of factors effecting on the value of a specific part of a route network and determines the characteristics and additional facilities and capabilities of that part an its nearby environment. Considering the variety of criteria in cost modeling these criteria are divided in to three groups of road, vehicle and humane factors (Table 1). Considering the short opportunity of preparing this paper and also the lack of sufficient information the modeling contains only some of the road criterion factors (Table 2)

The traffic rates, safety and security of the road, weather condition and road type are some examples of road criterion factors. The vehicle type and extent and type of fuel of that it use and … are examples of second group of factors which show the influence of vehicle in determination of the optimum route. The last group of factors is dedicated to humane factors including the age and skill of driver, the power of sight and familiarity of driver with car technical affairs.

Among above mentioned factors the road criterion factors are more general applicable in route finding analysis since the relevant information to this factors are more accessible than other two groups of factors. So in this paper we work on road factors on the other hand the weight of these parameters is also dependent on the vehicles types so the in the mentioned issues in this regard the cars are considered.

Table 1 – Criteria are divided in to three groups of road, vehicle and humane factors

Cost model criteria	example
Road criteria	Traffic, safety , additional facilities, weather condition, route length, geometric specifications, road type, road area, the potential points of collision, animals passing by, accurate driving signals, junctions and deviations, one-way or two-way direction, geographic direction, existent checkpoints
Vehicle criteria	Vehicle type and model, type and extent of fuel, vehicle weight, its shipment the method of tightening of shipment, the tires type, the lights, headlights, indicator lights and …
Humane criteria	Age, experience, fastening seat belts, wearing sight glasses, familiarity with car technical affairs, using road map and education and..

Table 2 – the road criterion factors which have been modeled in this research

Criteria	Sub criteria
Length	A main factor which was multiplied to other criteria in the structured model
Traffic	A, B, C, D, E levels of service
Safety	Like highway petrol centers, village and city points, side-road parking lots, z, health and medical treatment services, telecommunication centers
Tourism	Sea, lake and streams, dike, recreation places, jungle, mountain region, ski runs, cultural-historical places, antiques, religious regions, deserts, fishing zones,
Facilities	The fuel stations and public service centers and terminals
Weather condition	Moderate, relatively dry, cold , desert weather condition, warm and relatively dry, warm and humid

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