Night paving poses several challenges, most significantly safety. Crews are often working within a few feet of motorists whizzing by at high speeds, with the drivers' field of vision far more limited than during the day. The risk of a vehicle accident, according to AAA of Iowa and Minnesota, is also 40 percent higher at night. And as we age, our eyes are slower to recover from light glare, so motorists may be maneuvering the construction zones with even further impaired vision.
Another fact of night paving is it takes longer and is more costly to complete a project. "With the additional safety precautions and the setup and tear-down required, production is cut by up to 25 percent on a night job versus a day project," says Barry Rhinehart, project manager for the L.L. Pelling Co., North Liberty, IA. The extra equipment, flagmen and law officials to improve nighttime safety add to the project's cost.
Despite the safety challenges, Rhinehart says Pelling is seeing more night paving today than in the past. The growing popularity for nighttime road repair and construction can be summed up in one word: traffic. Around large metropolitan areas and heavily traveled interstates, traffic volumes are just too high for daytime paving.
"Reducing the number of lanes during the day creates too much congestion and traffic jams, which also pose safety issues," says Bill Rieken, paver application specialist for Terex Roadbuilding.
For Pelling in Eastern Iowa, nearly all projects on Interstates 80 and 380 will require some degree of night paving. The Iowa Department of Transportation conducts a traffic flow analysis of the proposed work zone prior to reconstruction in order to determine when paving can begin.
"For our current project on I-80 around Iowa City, we can start closing the lanes at 7 p.m. and have to be off the site by 6 a.m.," says Rhinehart. If the paving crews do not have all lanes open by 6 a.m., the company faces a penalty.
Turning night into day
Pelling's paving night begins with a safety meeting where the crew receives its safety gear; this includes American National Standards Institute (ANSI) Class 3 reflective vests and reflective leg bands. "Construction Ahead" signs are set up at the four- and two-mile markers ahead of the construction zone. Every night the signs and lane closure cones are set up and taken down, which cuts into Pelling's production schedule.
Light towers align the work area to help improve the field of vision and reduce the chance of light glare impairing a driver's vision. Iowa DOT metering rules stipulate the number and positioning of the light towers.
"The towers are required to keep a minimum light reading of five foot-candles at 50 feet from the equipment," explains Rhinehart.
In addition to the towers, parts of the paving train have light packages mounted to them. Pelling's paving equipment includes a Terex Cedarapids CR562 paver and an MS4 material transfer device. The paver is fitted with a 1,500-watt halogen light at each corner. And for mainline paving, two lights are mounted to the MS4 to help backing trucks align with the device's receiving hopper.
Trucks entering and exiting the paving area also have orange flashing lights on the sides so they are more visible to motorists in the construction zone.
Improving safety is just the first obstacle to night paving. Finding the additional power to operate the paver lights can prove difficult. Before the advent of electric screeds equipped with additional power and outlets, crews often had to get creative.
"With our older paver and diesel screed, we mounted a portable generator to the top of the paver's hood," says Rhinehart. "We would have to refuel it frequently during the night, which was inconvenient."
Paver manufacturers now offer auxiliary power kits for paving at night with diesel screeds. "Some manufacturers have a generator option, like the Terex Cedarapids pump package," says Rieken. "It will offer about 6 kW of power — enough to run night light packages."
Portable generators and optional pump packages are unnecessary with electric screeds, which include a generator with sufficient power to operate lights.
For example, prior to the 2006 paving season, Pelling purchased the CR562 paver equipped with a Stretch 20 electric screed. "The Stretch 20 has a 34-kW generator with three outlets and six plugs and a reserve of about 14 kW for powering night lights," says Rieken.
This lighting helps to make the construction zone safer, but it also throws shadows, which makes the roller operators' jobs much more difficult. It often takes more time to achieve spec densities at night. "It's harder for the operators to establish a rolling pattern since it's difficult to see where they finished their first pass," Rhinehart points out.
Screed operators also encounter difficulties during night operations. Holding the line while paving straight and at consistent depths poses little difficulties. But when the operator encounters a grade change or paves a "super" (sloped transitions in turns that allow traffic to maintain speeds), it's a different story. According to Rhinehart, it's harder to visualize and dial in the slope at night.
As traffic counts continue to grow on the nation's roadways, night paving will continue to be an increasingly larger part of roadbuilding operations, regardless of the challenges or costs. As such, crews will need to develop new tactics to safely delivera high-quality product, while relying on artificial light sources to turn night into day.