The Hokuriku region of Japan is known for its heavy snowfall, and clearing snow and ice from the expressways is one of the most important jobs of Central Nippon Expressway Company Limited (NEXCO Central). NEXCO Central is responsible for the full construction and maintenance of Central Japan’s expressways.
In addition to weather forecasts, the organization collects weather and road condition data from meteorological observatory stations and fixed cameras installed along the expressways, plus traffic management and snow and ice patrols. Managers plan their winter maintenance strategies and dispatch workers based on these data, and their decisions require extensive knowledge and experience with the region and its characteristic weather conditions.
It is essential to know the condition of road surfaces for effective snow and ice removal, which can be especially challenging since NEXCO Central is required to conduct these operations mainly at night. The organization already had meteorological stations in place, but these fixed-point measurements left observational gaps. Snow and ice patrols and traffic management personnel would visually check road surface and snowfall conditions to fill the information gaps. Black ice––which often forms overnight––is difficult to detect visually from inside a vehicle. In some cases, personnel would step outside the vehicle to check the road surface condition, which is a safety risk.
Salt spreading is a unique challenge in Japan, as it is necessary to use up all of the sodium chloride antifreeze agent once loaded into a vehicle. This is because drying agents and other additives cannot be added to it. The salt also contributes to bridge corrosion. To address these concerns, NEXCO Central works to minimize the amount of salt used by spreading just the right amount in the right place and time, a major challenge for any winter maintenance organization.
NEXCO Central started looking for ways to help fill the gaps in weather observation data and optimize salt use across the expressway network.
NEXCO Central introduced the Vaisala Mobile Detector MD30 to their road maintenance strategy through an extensive evaluation testing process, starting at their Kanazawa Branch. The Kanazawa Branch manages the Hokuriku, Tokai-Hokuriku and Maizuru-Wakasa Expressways — more than 340 kilometers (211 miles) of road.
The compact MD30 mobile sensor measures the key parameters essential to winter maintenance including surface state, grip, layer thickness, humidity, surface and air temperature, and dew point. NEXCO Central installed the MD30s on several winter maintenance vehicles for the evaluation.
The organization began by closely comparing various MD30 measurements with those of air and road surface temperatures collected from meteorological stations located in the field, along with grip measurements obtained by pendulum-style friction testing.
Takao Nakamura, Manager of the Quality Control Division at NEXCO Central, said "We obtained very high results for MD30 in the evaluation testing, with correlation coefficients of around 0.8 - 0.9 for all of the measurement items. Based on these findings, we determined that we could use MD30 to sufficiently supplement data for in between our fixed-point meteorological observation stations, which was the decisive factor in our decision to go ahead with full-scale deployment of MD30. Another key factor in our evaluation was that MD30 can produce not only numerical data, but also visual images that enable us to quickly ascertain road conditions."
Based on the device’s successful validation tests, NEXCO Central installed the MD30s on several winter maintenance of vehicles to consistently collect winter road condition data across the expressways.
The MD30 is installed on salt spreaders and other winter service vehicles, as well as the front bumpers of frequently used patrol vehicles. NEXCO Central is setting the MD30s to sample at 0.1s increments to make the most efficient winter maintenance decisions.
By transferring the MD30 data to their internal system, NEXCO Central expects to use the information for a variety of snow and ice clearing measures. Grip measurements, for example, are particularly useful for managing road conditions with objective numerical-based data. The organization is able to use road surface temperature information as a form of continuous data to provide a baseline standard for salt spreading operations. Dew point measurement is also very effective in determining freezing conditions without precipitation — common in the humid Hokuriku region.
NEXCO Central has significantly improved their methods for determining the state of road surfaces, especially at night. The organization can respond faster and more efficiently to changing conditions, leading to safer roads. With real-time data from the MD30, supervisors can issue instructions to maintain the expressways instead of risking personnel safety with visual inspections.
MD30 is contributing to NEXCO Central as they continue to provide safer expressways — for drivers and workers alike.