Does road improvement decrease greenhouse gas emissions?

In Norway, a debate has been going on about road improvement as an effective climate policy measure. In a report presented two years ago, it was concluded that there would be less greenhouse gas emissions in Norway if the road network were improved. Commissioned by the Norwegian Public Roads Administration, the Institute of Transport Economics has examined this relationship and arrived at a different conclusion. Road construction, largely speaking, increases greenhouse gas emissions, mainly because an improved quality of the road network will increase the speed level, especially in the interval where the marginal effect of speed is high (above 80 kms/h). Emissions also rise due to increased volumes of traffic (each person travelling farther and more often) and because the modal split changes in favor of the private car, at the expense of public transport and bicycling.