Wojciech Szymalski, 2016.11.26
Urban streets are ruled by Lewis-Mogridge position. This, so called, iron law of congestion, describes the relationship between the construction of roads and road traffic. According to Mogridge (1990) traffic expands to meet the available road space, what can be paraphrased in an everyday language:
the bigger the roads the worse are traffic jams.
The problem of traffic congestion in the motorized cities of developed countries has appeared in the 60s and 70s of twentieth century, when people began to notice the correlation between the road capacity and the number of cars moving on them. Apparently, during this period one of the greatest scholars of cities, American urban planner Lewis Mumford had expressed his view on city road construction programs quite bluntly:
Adding highway lanes to deal with traffic congestion is like loosening your belt to cure obesity. Since then, research on these compounds, as well as on the prediction of traffic continued. Polish engineers also took part in building a global knowledge on the subject. Already in 1983, Wojciech Suchorzewski, in his study on road system capacity in downtown Warsaw made assumptions later formulated as a Lewis-Mogridge position, ie.:
Travelling by car is so attractive that the car is used to the extent resulting from the capacity of the road and parking system (Suchorzewski, 1983: 24)
This means that traffic grows until the moment, when all the capacity of the roads and parking spaces in city is utilized. The results of this study are cited in subsequent sections of this article.
Lewis-Mogridge position was finally formulated after analysis of the relationship between the numerous investments and road traffic in London (Mogridge, 1990). The occurrence of this law notes that the streets are not isolated from the transport system and change in the parameters of individual sections is changing the whole system, not just this one street. This law also indicates the importance of the so-called: traffic (mobility) induced by the road investment and the need for the study and forecasting of this phenomena. A broad overview of the issue of induced traffic as a result of infrastructure investment has been made, among others, in the framework of the roundtable 105 of the OECD European Conference of the Ministers of Transport (1998).
Lewis-Mogridge position does not remain suspended in a scientific vacuum, and it is not a phenomenon that has been inferred without reliance on earlier theoretical work on the development of cities. Upon closer examination of the literature in this field, you can point out that this law is relating only to transport, but can be concluded on the basis on of much broader in sense threshold analysis proposed by Bolesław Malisz in the 60s of the twentieth century. Malisz (1963) found that while the number of inhabitants increases in a discreet way, public services in the form of urban infrastructure must be provided in a staggered manner, generating above-average expenditure relating to the crossing of the so-called: development thresholds. Staying in the sphere of transport considerations we can formulate a theoretical example of this observation. The existing capacity of the single carriageway road in the city is running out after 10 years from its opening, due to population growth, land use development and the subsequent traffic growth. As a result, the transport system capacity is the limit of city development. Thus, the city authorities decide to intervene by widening the road to two-lane double carriageway to give a stepwise doubling of capacity and development potential. Demand for car transport, measured by the number of cars per inhabitant of the city, which was reaching the level of single-lane road capacity at the time of the opening of widened road is twice lower than the demand that could fill a two-lane road. It is expected, therefore, that if the demand (number of cars per inhabitant) will grow at the same pace as before, the capacity of the two-lane road is going to run out for a minimum of 10 years. The development threshold have been broken and new growth capacity delivered according to Malisz theory. This theoretical reasoning is perfectly legitimate and correct, however, under certain conditions. The main condition is that the intervention (road construction) was done exactly at a time when the growth in car ownership and population, resulted in exhaustion of the road capacity of existing single carriageway road. The example described is a classic case of the land use cycle initiated by the construction of a transport link, which is shown in the figure below.
The process shown on the picture 1 have been described by Bronisław Malisz, but basing on his work we can draw a chart (picture 2) showing interdependence of development of the city (as a function of growing demand) with the development of infrastructure (a function of public services supply).
Described example is the positive effect, suggested by threshold analysis, which assumes that the city usually overcomes existing limits of development at the smaller or larger cost, depending on the time of intervention, because the number of urban dwellers is usually able to continue to grow. In contrast, Lewis-Mogridge position is part of the description suggested by the threshold analysis of Malisz in a way that signs a rather negative consequences. Let's take another theoretical example described below.
According to the threshold theory lack of infrastructure investment, restricts the further development of the land around it. Let’s assume that the single-carriageway from the first example is not extended. The city development either in demographic or transport indicators can still occur, although the costs may be higher and the rate of growth lower than if there was a road investment (Kuciński, 2000; Chmielewski, 2001). Without road widening the existing road capacity ends, but the city can still develop with its transport needs catered by different transport modes than a car or by a wider means of communication. Some needs cannot be met effectively through travel by car, so people and goods benefit from other means of transport, if they have access to: public transportation or bicycles or even walking instead of driving a car and creating traffic jams. In this case alternative modes of transport to the car are driving the development of the city. Some people, when the road capacity is limited, adapt, if possible, their behavior:
- Satisfying their needs locally rather than traveling further away, eg. at a local store, not in a supermarket a few miles away;
- Using the broad sense of communication instead of transport, eg. calling instead of hanging out with someone directly.
The needs of people are met, even though the demand for transport is therefore smaller. In the extreme case, with the shortage of alternative means of transport and when the less basic needs are at stake people resign from satisfying their needs or satisfy themselves rarely, eg. visiting relatives on the other side of the city every month instead of every week. It is a matter of philosophical discussion whether the disability to meet these and other needs is a restriction of development of the city.
Such a situation in our example – shortage of supply of road infrastructure – continues for some time that the demand for car travel is suppressed – traffic jams are frequent, but the potential demand is increasing. People around the road settle, establish new economic activities and perhaps even buy new cars, but they do not use them too frequently satisfying their needs rather through other modes of transport and communication. As a result, not fully realized the demand for travel by car along the exemplary road reaches the level three times higher as the road capacity. At this point the decision on expansion of road from one to three lanes is taken, to bust the city development and leave some capacity for the future.
The suppressed demand can now become an existing demand. On the opening day of the wider road everyone who has so far kept his car in the garage, tempted by the promise of faster and more comfortable driving on the new road, put the key in the ignition and leave. Suddenly, road with three times higher capacity is entirely occupied by cars and bad traffic conditions are similar to those prior to the investment. In this case Lewis-Mogridge position worked. All development opportunities which new road had to give, were once exhausted. Spatial development has been made before the investment, thanks to other means of transport than the car. Demand for transportation infrastructure supply was provided with too much delay. After the investment further development of the city will still have to be done by public transport, cycling, walking or through meeting the needs of people in a different way than by car. Using the threshold theory of Bronisław Malisz we can draw the chart below (picture 3) for this case.
Interdependence of demand and supply of public infrastructure in the case of car transport when road capacity is delivered with delay. Hidden demand for car travel is filled in by the car substitutes, which drive the development of the city. Own study.
Important in this theoretical example is the role of alternatives to road transport. The question arises, on the grounds of threshold theory, whether, the introduction of public transport in the city, after the exhaustion of the capacity of roads, is a way to overcome the threshold of development of the city or the necessary additional city maintenance cost arising in the city budget because of the undefeated developmental threshold, which is the exhaustion of the capacity of existing roads in the city? One thing is certain, the city's development is possible without increasing the role of road transport and can be controlled by stimulating public transport and other forms of transportation within the city.
It is time now to answer the question of how the considerations from the previous subheadings are to the road traffic of a particular city - Warsaw.
In 1983, Wojciech Suchorzewski assessed the capacity of the road system in downtown Warsaw with prediction for a year 1990. The professor stated that:
When the number of vehicles on the road network downtown at rush hour reaches 30 thousand cars, on almost 50% of the road network length traffic load will be close to the capacity or exceeding it (Suchorzewski, 1983: 38)
He considered this situation as a possible tolerance limit of the car user. Taking into account the assumption of Suchorzewski that in 1990 Warsaw will have 180-240 cars per 1000 inhabitants, it was calculated that the downtown Warsaw could be entered by a maximum 50% of a potential cars (50% of all of those, who would wish to do so). The remaining 50% of the cars, was a potential, suppressed demand for car travel in the city (Suchorzewski, 1983). In 2002, the average rate of car ownership indicator for the Warsaw city was already 411 vehicles per 1,000 inhabitants, and in 2012 - 580 vehicles per 1,000 inhabitants (GUS, 2004; GUS, 2014). It was twice as much than assumed by the professor. Thus, the demand for road transport in Warsaw is now even greater than in 1990, when it was expected to be impossible to enter all the cars to downtown because of the physical limitations of the existing space. So it can be concluded that in Warsaw Lewis-Mogridge position should work, at least in the area of the analysis of Suchorzewski from 1983.
Area analyzed by Suchorzewski was limited with the mileage of ring road, ie. Słonimski, Obozowa, Towarowa, Raszyńska, Batory, Spacerowa streets, as well as the Vistula river. Assumptions of the analysis provided for the construction of Trasa Świętokrzyska in downtown, together with a new bridge and widening of some of the inlets to the area, for example: Prosta street, which have not been realized to date. Thus it can be concluded that the supply of road infrastructure in the center of Warsaw is perhaps now a bit smaller than in the analysis of Suchorzewski.
One of the access roads to the city center, which during the last 15 years, much expanded, is Górczewska. In the years 1999-2006, expansion of individual sections of the road from city boundary to the downtown Warsaw continued. Górczewska ends up on the Młynarska Street bumping into Leszno Street, which leads further in to the Center. In 2013, an enlarged last section of Górczewska between the city boundary and Lazurowa was finished and opened (Osowski, 2013).
What was brought about by this expansion? First of all, on the entire route from the city boundary to Okopowa (Górczewska and Leszno Streets together) drivers now have 2x3 lanes and in selected places only 2x2 lanes to utilize, so theoretically the street capacity is 3000 vehicles per hour (calculated by the narrowest capacity segment). Previously, the street had cross-section of 1x2 lanes, it was a typical single carriageway two-way street.
According to the Lewis-Mogridge Position road traffic on this street should double as its capacity and this rise should be fast. This actually happened. Let's look at the numbers, from automatic measurements of traffic carried by the Authority of City Streets (ZDM) .
Table 1. Peak hour traffic (cars per hour) in direction to city centre for selected measurement points along Górczewska.
|Górczewska (city boundary)||Górczewska (middle circle)||Leszno (city center circle)|
Table 2. Road capacity utilisation for Górczewska middle circle measurement point.
|Road capacity (middle circle)||Peak hour traffic||Road capacity utilisation|
Table 3. Daily traffic (cars per day) in direction to city center for selected measurement points along Górczewska.
|Górczewska (city boundary)||Górczewska (middle circle)||Leszno (city center circle)|
Note: It was assumed that theoretical capacity of road lane is 1500 vehicles per hour according to the theoretical studies. It is true that with speed of 30-50 km/h, which occur mostly in the cities, theory foresees capacity in the range of 1800 to 2000 vehicles per hour, but in city traffic, there are additional capacity limitations resulting from flow disturbances caused by vehicle crossings, in particular with traffic lights, parking of vehicles and similar phenomena. For example, in Wroclaw the study
Analysis of capacity of roads in Wrocław Agglomeration (Via Regia, 2009) adopted the capacity of one lane as only 800 vehicles per hour (p.23 of the study), although noted that the capacity of two-lane dual-carriageway road in ideal road conditions is 1700 cars per hour for a lane (p.22 of the study).
ZDM measures the volume of traffic along the Górczewska Street in three points:
- on the border of the city (exit routes),
- on the bridge over the railway line (middle circle) and
- on Leszno Street (city circle).
These measurements show in 2006 a sudden, almost a twofold increase in the number of cars on the inner circle, from approx. 1400 vehicles per hour on average during the peak morning hours during the 6 years prior the investment (2000-2005) to the app. 2400 vehicles per hour on average during the peak morning hour in over the next six years after investment (2006-2011), with no further upward trend. On a daily traffic it was an increase from approx. 15,000 cars a day to 25,000 cars daily. What caused this increase? In 2006 the widened section of Górczewska Street between Silesian Insurgents Street and railways at Wola Park, when the measurement point lies was opened. From this year Górczewska on its almost length has 2 carriages with 3 lanes each (Osowski, 2013).
However, this increase in traffic could happen due to the transfer of cars from other streets to the wider Górczewska. Such thesis can be easily dismissed by the measurements of the ZDM on middle circle point of the nearest streets parallel to Górczewska. Neither on Squadron 303 Street nor on Połczyńska Street the traffic significantly dropped in 2006.
Table 4. Peak hour traffic on Górczewska and neighbouring measurement points (cars per hour).
|Górczewska (middle circle)||Dywizjonu 303 (middle circle)||Połczyńska (middle circle)|
Widening of Górczewska Street was done to avoid traffic jams, but instead more cars was able to get into the city center of Warsaw and traffic jams are even bigger. 2400 cars per hour makes 80% of Górczewska Stret capacity and yet this capacity is limited with the traffic light at the intersections. This means that traffic jams may occur on Górczewska frequently, with more car on the road than before. Lewis-Mogridge position works!
The example of Górczewska Street is located outside of the area analyzed by Suchorzewski in 1983, which shows that the current 'hidden' demand for car transportation in Warsaw can cause Lewis-Mogridge position working throughout the city, not just downtown. Besides, such a finding is not only justified with this example, but it is an outcome of an analysis of 12 years of road investments (from 2000 to 2012) in Warsaw, conducted as part of a series of articles titled: "Lewis-Mogridge position in Warsaw" (Szymalski, 2014). This cycle showed that Lewis-Mogridge position in Warsaw is working:
- for investments close the downtown of the city, for example Świętokrzyski bridge; and
- on the city boundary, for example Modlińska Streets and Łukasza Drewny Street.
The diversity of the analyzed investments also shows that Lewis-Mogridge position may occur regardless of whether extension of capacity is made:
- on the road leading to the city center (Górczewska), or - having the nature of bypass (Siekierkowski Bridge and Highway),
whether it is
- increasing the capacity of the intersection by the construction of flyovers (Roundabout Starzyńskiego), or
- the construction of a new bridge (Curie-Skłodowska Bridge).
Lewis-Mogridge position occurs in urban areas wherever the potential demand for traffic is higher than the capacity of the road system. Such situation is a fact in Warsaw as it was showed earlier on figures relating to the number of vehicles per 1,000 inhabitants. In such places the determining factor for the intensity of traffic is the road infrastructure supply, not the demand for car travel. Demand may in fact be realized only to the extent of supply, which is provided by the infrastructure, whereas the excess of demand is not realized and creates a potential, hidden, suppressed demand. As a result, when implementing transport policies much less important are the factors affecting road traffic such as:
- An increase in the number of inhabitants of the city and the individual districts;
- An increase in the number of vehicles (expressed with an indicator of the number of cars per 1,000 inhabitants);
- Increase in the number of destinations (eg. new shopping centers);
- The availability of fuel (measured by the price of fuel);
- The availability of (or a must!) alternatives to car travel.
Because all these factors influence the demand for car travel in the city, which for the most part cannot be realized due to limited supply. Generalizing the previous deliberations and conclusions steaming from the fact that Lewis-Mogridge position works in urban areas a drawing can be constructed, which indicatively shows the ratio of demand to supply as a function of the position of the road in relation to the urban area.
As can be inferred from the figure road investment has a chance to trigger appropriate land use cycle outside the city, where no excess of demand for car travel exists, so Lewis-Mogridge position, too. Such land use cycle can be observed today, eg. along the S8 from Radzymin to Wyszków, which was put into service in 2008 and attracts new investors. This land use cycle was active in Łomianki from the 70s of the twentieth century, when the bypass of S7 road was built around it. A set of maps have been prepared to show, how the new development were moving Łomianki closer to the road build in 1974. Roads can generate development in such circumstances.
Łomianki spatial development in a set of topographical maps. 1936-1956 – the development sticks to the old road and to the North of it, railroad which existed in 1936 is visible in 1956 as unused bank. 1977-2012 – the development moves south to the new road bypass placed on the site of old railroad and constructed in 1974, later new buildings take both sides of the new road. Own study.
In contrast, in the city the development is generated by public transport, cycling and walking - land use cycle is continued after the exhaustion of the capacity of road infrastructure. The best example of this type of development are new settlements arising after the final opening of the Warsaw metro line nr 1. In 2002-2006 flourishing development activities took place in Kabaty upon completion of subway line in the course to the city Center, and from year 2008 the development moved to Bielany, when the metro line was finished. Higher development of new buildings was caused also by integration of city public transport and railway ticket tariffs in 2008. In this case mostly Rembertów, Włochy and Ursus districts benefitted however, no new road investments were made connecting this districts with the city center. Warsaw "City", which is a quarter of high buildings restricted by Emilii Plater, Al. Jerozolimskie, Al. Jana Pawła II and Świętokrzyska Streets, was also created mainly by the existence and improvement of public transport in the area: Central Station, subway line nr 1, tram networks - road network expansion has not been here for a very long time. More and more workers of this type of office areas commute to work by bike, and business and entertainment needs they enjoy on foot in the nearby bars and shops.
Chmielewski Jan Maciej, 2001, Teoria urbanistyki w projektowaniu i planowaniu miast, Oficyna Wydawnicza PW, Warszawa
GUS, 2004, Rocznik Statystyczny Warszawy, Warszawa
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Malisz Bolesław, 1963, Teoria progów – jej rozwój – zastosowanie i perspektywy, Biuletyn IUA, nr 16-17
Mogridge J.H. Martin, 1990, Travel in towns: jam yesterday, jam today and jam tomorrow? Macmillan Press, London
OECD, ECMT, 1998, Infrastructure-Induced Mobility, 105 Round Table, Paris
Osowski Jarosław, 2013, Poszerzają Górczewską już od 12 lat. Wreszcie skończą?, Gazeta Stołeczna, Warszawa,
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Stover Vergil G., Koepke Frank J., 2002, Transportation and Land Development, Institute of Transportation Engineers, Waszyngton
Szymalski Wojciech, 2014, Prawo Lewisa-Mogridge'a w Warszawie, [zobacz >>>]
Via Regia Plus, 2009, Analiza przepustowości szlaków komunikacyjnych Aglomeracji Wrocławskiej oraz Badanie potrzeb transportowych przedsiębiorców Aglomeracji Wrocławskiej, Analizy wykonane na zlecenie Biura Rozwoju Gospodarczego Urzędu Miejskiego Wrocławia w ramach projektu Via Regia Plus, Wrocław
Author: dr Wojciech Szymalski, Institute for Sustainable Development.
Key words: Lewis-Mogridge position, development of a city, land use, induced mobility, Warsaw.
Article published in: Kuligowski W., Stanisz A., Cultures of Motorway: Localities Through Mobility as an Anthropological Issue, Poznańskie Studia Etnologiczne 19, p. 139-152, Wielichowo, 2016.