A change in the maximum speed from 50km/h to 40km/h on Lisbon’s roads is currently being discussed. The answer to this question is not obvious and depends on several factors. First, it is necessary to realize that the underlying network has a hierarchy, this hierarchy that has to be well in the city’s plans. There are at least arterial roads, local roads, and you can work with more maturity levels of your objects. In Lisbon, there are already 30km/h neighborhoods, for example. In general, at each level of this hierarchy, etc., comparing differences in dimensioning to maximum speed, number of lanes and existence of a segregated lane for other modes: BUS lanes, cycling lanes, etc. access to mobility and public space. The change from 50km/h to 4km/h does not have to be at a road level for this issue, as it can be applied to specific lanes of the network if desired, for example, to solve accident ratio problems or to protect the installation of lanes. cycleable.

It is clear that a reduction in speed always leads to a greater one, and it is possible to build a very significant relationship between speed and speed. severity of a change. But, as with everything in life, there is always a replacementbetween risk and objectives of a given decision. That there are road accidents would certainly be enough for everyone at home, so that there is no way for us to occur during the pandemic. It is therefore necessary action applied to a specific study in the search for the city’s road model to understand that the decisions applied to selected alternatives and proposals. not enough for that a study of the kind like the reduced one that is referred to in the newspaper, a study that makes no sense for an incomplete economic analysis of speed in the city, making unrealistic assumptions about mobility. A saber:

• Vehicle occupancy is defined at 1.6 people per vehicle, which is the result in the survey carried out by INE in the Lisbon Metropolitan Area. One study of the problems with this approach is that many trips are carried out with children, so the study is assigning them a salary, when they associate a salary-based time value (see next point).
• Time value is fully indexed to salary. However, we know that the economic value of time inside a vehicle on a commuting trip depends on the salary, but also on the experience of the trip. Rarely is the average salary used for the value of lost time because not all travel time can be converted into salary time. As an example: the average commuting time in the Netherlands is around 10 euros per hour, in population surveys, but the average salary in the country is more than 20 euros per hour. So the salary is twice the value of time. The value of time only starts to be very high when the trip is carried out during working time, that is, when the company is directly paying the worker for that time. However, these trips are fewer in number when commuting.
• The travel distance is defined as 15 km. But this is the average distance; if the averages would be for doing transport studies, I wouldn’t work on one with 30 professors developing models for decision support in traffic and transport. This is a crude approach that is not given the importance limitation of speed reduction.
• The costs are not economic Nothing is mentioned here about the cost of cities and studies of human lives that could be saved with a reduction in speed in certain axes of life. It is necessary to bear in mind that the reference values ​​for human life in terms of cost-effectiveness in transport are quite high in the European Union. This value is indexed, namely, to the loss of productivity of the individual who loses his life in traffic.

However, it is right when mentioned, from the point of view of engine operation, the highest efficiency is not found at speeds of 40 km/h, in vehicles that are between 50 km/h and can be between 80 km/hh To list this statement, correct, refers to speed another technical study that relates to engine efficiency and contact. these values ​​are determined in an ideal circulation situation. In urban areas, there are other factors that play a very important role in road capacity (number of vehicles per unit of time that cross the cross section of an environment) and such as flow stability, creation of bottlenecks (bottlenecks), and number of intersections with other roads and lanes.

Finally, it remains for me to explain that in transport, a measure can never be long term, only in the context of a short term static without medium and long term effects. There are many examples of problems that do not increase, however, from congestion to car problems and do not worsen them, only the problems of congestion. This is because the mobility system and uses of individual and long-term transport mode can be adapted to people in the medium term, because the devices are changing, for example, because the location mode of your residence is changing or changing the location. By reducing the speed, it is not clear to other preferred modes of transport, namely the modes that will thus be more protected to a gradual change, in the distribution of the most protected form by the modes radically, in the distribution of the preference for the different modes.

The conclusion that “The decision to reduce speed in Lisbon will have a negative impact on the environmental, per se and social level” in the study is thus well founded as a negative impact of much more analysis limits on all the above factors. Carlos Barbosa from the ACP said – and I couldn’t agree more with him, on this subject – that “Without studies, you can’t take such measures.” The problem is the quality of these studies. I believe that the CML is now prepared to answer this question with results from the transport models that have been developed as well as the data they collect in real time from traffic. These, and only these, are the results that are needed to be incorporated into an analysis of economic economics, not the use of average values ​​taken out of context. Unfortunately, and for a long time now, a detailed survey of the mobility of the inhabitants of the Lisbon metropolitan region has been lacking for the best transport models.

It is a pity that the discussions in Portugal continue at a very low level. Nobody offers suggestions for conducts in the water pipe network in the city of Lisbon but everyone has an opinion about the road network, technicians as if they were not knowledge to plan and manage transport networks. Some press doesn’t help. Recently on P3 do Público it was said of an International Relations student living in Lisbon for a year: “Before starting the Madrugada Network project [da CARRIS], its portfolio was already quite composed, having redesigned, for example, the map of the Lisbon Metro. That’s why he arrived in the capital, in September 2021, he already had all the metro stations in his head”. The idea that the subway network can be designed as a hobby is as much better as it is dangerous, because it may be that in the near future we will only be left with amateurs for planar transport networks in Portugal, whatever their intentions and “eye” are. for public transport”.

As for the issue of speed reduction, Livre says that it is now the Chamber that has to study the problem. And as political as I seem interested in seeing the results of such a study, this is a pernicious way of looking at it. The assembly determines in relation to which it does not know the true result, but it is the councilor who has to justify it. We run the risk of the largest chamber being governed by decree in the country from the municipal assembly. Anyway, understand each other.

Gonçalo Homem de Almeida Correia holds a PhD in transport from the Technical University of Lisbon (Instituto Superior Técnico) and aggregated in transport systems from the University of Coimbra. He has a university career spanning over 12 years and is currently Professor at the Technical University of Delft, The Netherlands, and Visiting Professor at Peking Jiaotong University in Beijing, China, in its engineering and transport engineering programmes.