Locating Road Meteorological Stations Using Analytical Hierarchy Process Method (Case Study: Alborz Mountain Roads)

Introduction
Roads are part of civilizations’ development. Not only do they support economic activities, but they are the foundation of new life. However, it is quite unfortunate to note that in the last decade due to low driving culture, non-standard vehicles and roads, environmental factors, and increasing traffic volume, number of road accidents have increased dramatically. Four factors of human, vehicle, road, and environment are always responsible for occurrence of accidents. Among these environmental and climatic factors that happen due to particular geographical conditions of Iran and its mountainous nature, along with other factors play a significant role in accidents. Major road meteorological tasks for both land and rail transportation are one of the most important issues at a national level. These involve continuously preparing statistical data and information; changing and evolving meteorological elements in the area of roads covered by the relevant station; issuing specific meteorological forecasts along the route in relation to wind intensity and speed, thunderstorms, and occurrence of destructive phenomena; and publication of notices and warnings in the event of dangerous weather phenomena on the way, intense winds on various stairs, and phenomena that are effective in reducing the vision. The aim of this study is to locate the meteorological stations of the Alborz Mountains axes (Chalus and Haraz) using the Location-Allocation method.
Materials and Methods
The study was conducted in the mountainous roads of Alborz (Chalus Axis and Haraz axis). The criteria used to locate road meteorological stations pertained to the climate (rainfall above 30 mm, avalanche, snow cover, fog, and minimum and maximum temperature of -10 and 30 degrees Celsius), geomorphological aspects (rock fall, landslides, and active faults), traffic (accidental points and environmental criteria), and economic security (traffic). Then, using the Analytical Hierarchy Process (AHP) method, based on the determination of variable comparison matrix and weighting each criterion, the final prioritization map got prepared in accordance with the final weight. Afterwards, based on the Location-Allocation Analysis, the proposed meteorological stations on the mountainous axes of Alborz were determined.
Results and Discussion
Three meteorological stations of Karaj (from Karaj to km 43), Siah Bisheh (km 43 to 110), and Nowshahr (110 km onwards) reflect the climatic conditions of each section. The number of days recorded for fog occurrence at Siah Bisheh Station was approximately 844 days in a decade-long duration, while Nowshahr and Karaj Stations had 70 and 50 foggy days, respectively. Therefore, about 43 to 110 km of the road had the highest probability of foggy days, according to the statistics of Siah Bisheh Station.
As for the case of frost, 60 to 100 km of the road, from the city of Karaj (middle part of the axis) was riskier than the rest. From the beginning of the axis to 60 km, approximately the area between Vali-Abad and Marzanabad, the risk of frost was moderate. In other parts of the axis, the intensity of frost was either low or very low.
Chalus Axis in Mazandaran Province, from approximately the area of Vali-Abad village to Chalus City itself, included high and very high risks of rainfall above 30 mm, whereas in Alborz Province it experienced low rainfall risk conditions.
Due to the minimum temperature threshold of the middle part of Chalus Axis, involving two provinces of Alborz and Mazandaran, it was in moderate danger. This part of the axis included Nesa, Gachsar, Siah Bisheh, and Harijan. Other parts of the axis belonged to the low risk class. Yet, due to the maximum temperature threshold in Chalus Axis, the hazardous conditions of the axis were low in Alborz Province and very low in Mazandaran Province.
Examining the average snow cover by the desired months in this study, it can be seen that the middle parts of the Chalus Axis experienced the highest frequency of snowfall. Come the warmer months of the year and a gradual trend of snowmelt could be observed.
In terms of avalanche risk, the area of Asara village had a moderate risk, while the central sections, from Garmab village to Zangoleh Bridge, fell under high and very high classes. From the Siah Bisheh Area until the end of Chalus Axis, the avalanche fell to the low-lying class.
The 74 km, 78 km, 82 km, 84-85 km, and 88-89 km points from the beginning of the axis had been reported to be affected by landslide phenomenon. In terms of point density, at 78 km to Chalus in Mazandaran Province had the highest amount.
The maximum number of accidents took place either at 17-20 km or 41 km from the start of the axis in sunny weather; at 62 km in cloudy weather; at 40 km or 70 km during the rainfall; at 40 km, 60 km; at 62 km in snowy weather; and at 60 km, 62 km, and 65 km during the foggy weather.
The importance of each criterion and sub-criterion got determined in accordance with library studies, installation guidelines for road meteorological stations, and expert opinions. The uncertainty coefficient was also 0.6, less than the defined 0.1. Based on this result, the weighting process was approved. According to global standards as well as conducted studies, the distance between meteorological stations on the road varied between 30 and 50 square kilometers. In general, each meteorological station could cover an area of about 30 km.
Then, using AHP Method, the final weight of climatic, geomorphological, traffic, and economic-security criteria and sub-criteria in Haraz and Chalus Axis were determined. After prioritizing the new stations in terms of need in the previous step, through Location-Allocation Analysis as well as examination of optimal distances of the axis from the highway, fuel stations, surveillance cameras, and villages around the axis, the final stations were introduced in a priority-oriented fashion.
Results
Due to the importance of optimal development of road meteorological network, which reduces road casualties, damages the surrounding environment, and brings about economic savings, the optimal location on Chalus and Haraz Axis was examined. Results showed that the required stations on Chalus Road are in the area of Kiasar, Marzan Abad, Khargoosh Darreh, and Vali Abad and inside Haraz Road in Polur, Abali, Rahdari, and Rineh.