The pollution level has been evaluated through air quality indicators such as CO levels, NOx levels and particulate levels. The City of Aalborg has used a framework for air quality modelling developed by DMU (National Environmental Research Institute), organisation that also carried out the modelling.
Also vehicle emissions are indicators for knowing the effects of this measure. The emissions from vehicles have been modelled based on a licence plate registration carried out after the implementation of the Environmental Zone and compared with data from before the implementation.
The results from the modelling show a reduction in emissions as an impact from the introduction of the environmental zone.
The share of trucks with Euro IV or better increased from 28% in 2008 to 54% in 2010. The trucks with engine standard Euro II or earlier have been reduced from 26% to 15%. There has been a replacement of both Euro II and Euro III vehicles. Euro II vehicles are having an age where they are normally replaced rather soon. The registered trucks are on average 6 years old. According to Statistics Denmark, the average age for the entire car park in Denmark in 2010, is 8.2 year for trucks.
Finally, it can be argued that Aalborg's image as an environmental conscious city is improved. And furthermore it might increase, or be a prerequisite for, the migration of people, companies and students to Aalborg. These impacts are not easily quantified, but should, none the less, be taken into account when evaluating the success of the measure. The same goes for the documented decrease in NO2 reductions.
The overall conclusion from the process evaluation is that LEZs are realistic, when they are introduced according to national policy. If national policy allows a LEZ installation and if the city has the required stakeholder support then a consideration of a LEZ makes sense.