Tag Archives: street space

Urban tramways and surface transit priority – Paris

The biggest drawback to any surface transit line is the inherent conflict at the surface with other modes: cars, bikes, pedestrians, etc. This is an inherent element of competing for the same real estate as other priorities. When space on the surface is simply overtaxed or too contested, urban transport networks can add layers – but usually with great expense. With their tramways, the French manage to blur the lines between upgraded legacy street-running tram networks and the American conception of light rail as a kind of rapid transit.

In France, transport planners work to maximize the efficiency of surface transit operations to provide cost-effective transit network expansion. Standardization and relatively low costs allow a wide range of cities  (including the Paris region) to afford investments in new services.

Two of the Paris tramways illustrate the flexibility of the mode and the opportunities for efficient surface transit: The T2, operating on a repurposed rail right of way; and the T3, the first modern tramway in the city since the 1930s.

T2 at the Belvedere station. Note the alingment within the old rail right of way; La Defense skyscrapers in the background. CC image from Wiki.

T2 at the Belvedere station. Note the alignment within the old rail right of way; La Defense skyscrapers in the background. CC image from Wiki.

Community gardening spaces in unused right of way adjacent to the Belvedere T2 station. Photo by the author.

Community gardening spaces in unused right of way adjacent to the Belvedere T2 station. Photo by the author.

The T2 Tramway makes use of old SNCF rail right of way, but uses trams to allow for surface-running extensions at both ends of the line. The old suburban rail line closed in 1993, with the replacement tram service beginning in 1997. The line has since been extended in 2009 (into Paris) and in 2012 (north of La Defense).

The line’s  regular and frequent service has proven to be popular, carrying 115,000 riders daily. After blowing the initial ridership projections out of the water (as well as the ridership for the old suburban service that ended in 1993), the offering of frequent service along the same line (4 minute peak headways) shows what a difference a solid, frequent service plan can bring. In 2003, RATP had to lengthen the platforms (to 65m) to accommodate double-length trains.

Between the dedicated, mostly grade-separated right of way, platform/train length, and train frequency, the level of service comes as close to the Paris Metro (most Metro station platforms are 75m long, save for the busiest lines and key transfer points) as you can get while remaining on the surface.

Looking across the T2 platform to a Transilien train at Puteaux. The fence forces passengers to use the faregates to get on a Transilien service. Photo by the author.

Looking across the T2 platform to a Transilien train at Puteaux. The fence forces passengers to use the faregates to get on a Transilien service. Photo by the author.

The line’s heritage as a mainline railway is on display at the Puteaux station, where a cross-platform transfer is available to the L and U Transilien services. A fence along the platform forces those wishing to transfer to use faregates, meshing the tramway’s proof of payment system with the faregates found on the Metro, RER, and many of the suburban train stations.

The 2009 extension of the T2 brought the line into Paris, proper (incidentally, connecting to the T3 at Porte de Versailles, one of the areas of Paris slated to allow taller buildings), leaving the old SNCF right of way in favor of running on city streets. True to the standards established with other tramways, the trams are always given their own, dedicated right of way (often with grass tracks, both as a nice urban design touch and as a way to keep cars and trucks out).

Paris T3, showing street section with grass tracks. Photo by the author.

Paris T3, showing street section with grass tracks. Photo by the author.

At Porte de Versailles, riders can transfer to the T3 line. The modern tramway takes advantage of wide Parisian streets. Station platforms provide ample space compared to the legacy platforms in Amsterdam; two lanes of traffic in each direction move freely; sidewalks are wide with ample space for walking. Unlike the T2, the construction of the T3 involved removing car capacity in favor of transit.

Stop spacing is fairly close by American standards, but not for Paris – 500m on average. Similar to the T2, trains operate every 4 minutes during peak hours. Compared to the previous bus service along the route (averaging 15 kph), RATP claims the T3 is faster, averaging 19-20 kph (about 12.5 miles per hour). By comparison, almost no WMATA bus routes in the core of DC get above 10 mph average in the AM rush hours, and the PM rush is worse.

Not only does the T3 represent an improvement in speed and reliability over previous bus services, but it also adds capacity over bus. Like the T2, the T3 is also popular, exceeding ridership estimates. Riders strain the system, and operating along the surface, adjacent to traffic presents risks to speed and schedule adherence, despite signal priority for transit. Perhaps fewer stations with wider spacing would provide for faster average speed, but aside from that kind of change, it’s hard to see how you could squeeze more out of surface transit than the T3.

At the same time, the T2 shows the flexibility of tramways, allowing for mixed operation on surface streets as well as dedicated, grade-separated right of way. Where well-placed existing right of way (like the T2) isn’t available, there is also the option of pursuing a Premetro strategy, taking advantage of incremental implementation of full grade separation. The same vehicles can be used in both schemes; allowing flexibility not usually available to a Metro system or suburban rail.

Urban tramways and surface transit priority – Amsterdam

As impressive as the European subway and mainline rail networks are, recent expansions and improvements to surface transit networks are also noteworthy. Examples include upgrading legacy tram networks and building new networks on existing streets, as well as new uses for old mainline rail rights of way. Each example shows different methods of providing priority for surface transit.

In Amsterdam, the challenge is to provide priority for high-capacity modes along constrained city streets. The methods of providing surface transit priority complement efforts to create a pleasant walking environment and to preserve the city’s urban design and historic canal network. Together, these policies present a virtuous cycle – prioritizing transit, biking, and walking makes each of those modes more efficient and thus a better alternative to driving; which in turn lowers opposition to limiting the role of the car, making it easier to implement priority for surface transit.

Not all of this prioritization is the result of active choices; Amsterdam’s city streets vary tremendously in width. The city’s canals limit available street space, providing a natural limitation on cars within the historic city. Unlike other cities, Amsterdam largely did not remove its pre-war network of trams. Thus, the city retains the benefit of the old infrastructure network, but does not have the option of easily recrafting large rights of way with entirely modern tramways, as we see with modern tramways in France. Today, the network is extensive both inside and outside the historic city core.

Center-running tramway in Amsterdam. Photo by the author. Image links to Google Streetview of approximate location.

Center-running tramway in Amsterdam. Photo by the author. Image links to Google Streetview of approximate location.

Within the historic core, many services often converge on a core trunk line located along the broad avenues without canals. In the case above, the trams use a dedicated, center-running transitway (many of Amsterdam’s older trams do not have doors on the left side of the vehicle). Passengers load from side platforms on islands in the street.

The remainder of the street cross-section (visible on the far side of the above photograph, and in Google Streetview) includes one travel lane and a bike lane in each direction. In the tree zone, several parking and loading spaces are included along the street. I witnessed several loading vehicles double-parked in the travel lane, but the physical divider between the transitway and the general traffic lane is low enough that a car can easily navigate around a loading vehicle; car traffic in general is low enough that this does not greatly congest traffic or transit.

Gauntlet track in Amsterdam's Tram Network. Image from Google Streetview.

Gauntlet track in Amsterdam’s Tram Network. Image from Google Streetview.

Other links in the network run perpendicular to the city’s rings of canals; old narrow streets sometimes require gauntlet track. These streets represent the Dutch movement towards shared environments; the rails and pavement tell pedestrians where the trams run, but pedestrians walk all along the street and move out of the way as trams pass. Car traffic is allowed, but generally limited to service/delivery vehicles without limiting transit service – an outcome possible due to the general limits on car traffic.

Amsterdam tram in mixed traffic, with floating bike lane and on-street parking. Photo by the author.

Amsterdam tram in mixed traffic, with floating bike lane and on-street bike parking. Photo by the author.

Other streets involve streetcars in mixed traffic. The example above shows the tram platform ‘floating’ away from the curb to allow the bike lane passage along the street (at the expense of sidewalk width). On the far side of the street, there is a painted bike lane (red/maroon) and extensive in-street bike parking. An older Google Streetview of the same location shows that space used for on-street car parking; it also shows the wider sidewalk (with enough room for two-seat tables in sidewalk cafes), thanks to the trams in the other direction utilizing a station just around the corner.

Dedicated tramway near the Rijksmuseum in Amsterdam. Note the allowed taxi usage of the transitway. Photo by the author.

Dedicated tramway near the Rijksmuseum in Amsterdam. Note the allowed taxi usage of the transitway. Photo by the author.

Where the space is available, trams are given dedicated right of way. This example, near the city’s Museumplein, features a center-running transitway, landscaped buffer, general traffic lanes and bike lanes differentiated by color. The image also demonstrates the city’s policy of allowing taxis to make use of transitways to speed the journeys of shared-use vehicles.

On-street parking is available, but it isn’t really on the street – parking occurs by the car mounting the angled stone curb in designated areas. In the immediate foreground of the image above, you can see the outlines of an empty parking space (designated by gray pavers). Thus, when not in use, the empty parking space becomes part of the sidewalk rather than part of the street.

All of these different kinds of prioritization (along with the famous Dutch investment in cycling infrastructure) come together to influence the city’s transportation behavior. One of the key slides in this presentation from Rene Meijer, deputy director of traffic and transport in Amsterdam, shows not just the city’s mode share, but also the varying mode share based on the distance of travel:

Mode share for Amsterdam residents, both pre trip and per km.

Mode share for Amsterdam residents, both pre trip and per km.

As you might expect, most trips are shorter trips; longer trips will require modes suited for longer trips (rail; transit; car). Walking comprises 24% of all trips, while only accounting for 2% of the distance covered.

Amsterdam Mode Share by trip distance.

Amsterdam Mode Share by trip distance.

Breaking trips into reasonable distances, you can see how each mode has strengths in certain distances. The white bars show walking dominating short trips (up to 1km), where biking then explodes. For longer trips in the window of 5km to 20km, transit (with priority) and car travel both grow. Also, while intercity rail and transit are presented as separate modes here, actual behavior may involve similar kinds of trips, thanks to the integration between the two modes within the Dutch rail network.

The chart does not differentiate between destinations; I would hypothesize that transit performs better for trips to destinations that are well-connected to the transit network, and the same is true for auto trips. The Netherlands have good highways, but they wisely do not penetrate the historic city core, nor would one volunteer to drive along Amsterdam’s canals when so many better options exist. Even at very long distances, the difference between trains and cars likely depends on differences in origin/destination: the kind of land use, the ease/difficulty of auto/transit access, and so on.

Just as the Dutch have invested in bikes and unsurprisingly end up with strong bike usage, the same can be said of transit. While the optimal distance of effectiveness for bikes and transit likely overlaps a great deal, Amsterdam shows ways to meet both goals.

Speed, urban transportation and geometry heuristics

Following up on this previous post, noting that “transport is mostly a real estate problem” – a few quick heuristics on cities, speed, and space:

Comparison of population/employee density and street area per person. Image from NYU Urbanization Project.

Comparison of population/employee density and street area per person. Image from NYU Urbanization Project.

Regarding speed: 

Speed requires space; faster travel occupies a larger area than slower travel.

Speed alters our perception of space. Faster travel makes large things seem smaller (hat tip to this post from GGW for the links). The properties of the space affect how we use it and what we percieve it to be; wider roadways within streets get used for faster travel.

Regardless of speed, cars require large spaces relative to their capacity. Even when parked (v = 0), cars require lots of space. By extension, building cities around requires a completely different spatial footprint.

Regarding space: 

There is a strong tendency for cities to devote about 25% of their land to streets. Street networks are for mobility, but also for access to land. Devoting too much land to streets is wasteful; too little makes it difficult to unlock the value of the land within a city.

Intersection density correlates with walkability and connectivity; wider instersection spacing correlates with the higher speed travel of cars.

Consider the relationship between the density of the network (intersection density), the tendency to use ~25% of land for streets (regardless of the density of the place), and street width on the kind of transportation.

Simply requiring some minimum intersection density for new developments via a code will still be subject to ‘gaming’ and open to unintended consequences.

Street networks are sticky and tend not to change once established; the cities that grow around them are path-dependent. However, transport networks can be layered – subways travel fast, require space and grade-separation, but deliver passengers to the street grid as pedestrians; just as freeways are layered above/below streets and deliver high volumes of cars to local streets.

While the physical space allocated to streets tends not to change, the use of that space can change a great deal over time.

More on the geometry of transportation: “Transport is mostly a real estate problem”

In June, the Urbanization Project at NYU’s Stern Center posted several graphics looking at the space devoted to transportation in our cities. As the author, Alain Bertaud, frames it, “transport is mostly a real estate problem.” That is, different transportation modes require different amounts of space to accomplish the same task.

Comparison of population/employee density and street area per person. Image from NYU Urbanization Project.

Comparison of population/employee density and street area per person. Image from NYU Urbanization Project.

Each of the selected examples cluster around the diagonal blue line, representing an average of 25% of a city’s land devoted to streets.

Percent of land use devoted to buildings, streets, etc. Image from NYU Urbanization Project.

Percent of land use devoted to buildings, streets, etc. Image from NYU Urbanization Project.

Two observations: the 25% pattern is remarkably consistent; as is the geometric relationship between modes of transport and the intensity of land use.  The green horizontal lines show how much space a car uses at various speeds – the faster the car goes, the more space it requires. A parked car occupies 14 square meters, while one moving at 30 kph takes up 65 square meters.

The obvious corellation is between a city’s density and its type of transportation network. Cars take up a large amount of space relative to their capacity, and a transport system based on cars alone cannot support a great deal of density.

Alex Tabarrok frames this in terms of “the opportunity cost of streets.” While there is certianly an opportunity cost to various street uses, it’s worth noting that some space must be devoted for streets in order to access property. Charlie Gardner at Old Urbanist takes note that the role of streets is not solely about transportation:

In addition to their transportation function, streets can also be understood as a means of extracting value from underserved parcels of land.  The street removes a certain amount of property from tax rolls in exchange for plugging the adjacent land in to the citywide transportation network.  Access to the network, in turn, increases the value of the land for almost all uses.  For the process to satisfy a cost/benefit analysis, the value added should exceed that lost to the area of the streets plus the cost of maintenance. (This implies rapidly diminishing returns for increasingly wide streets, and helps explain why, in the absence of mandated minimum widths, most streets are made to be fairly narrow.)  For many of the gridded American cities of the 19th century, as I’ve written about before, planners failed to meet these objectives, although these decisions have long since been overshadowed by those of their 20th century successors.

Charlie also notes that many great, dense, walkable cities around the world devote about 25% of their land to streets, yet many American downtowns use a much higher percentage of their land to streets.

Some of those numbers might depend on the exact method of accounting. While Charlie’s estimate for downtown DC shows 43% of the land used for streets, DC’s comprehensive plan shows approximately 26% for the city as a whole:

Land Use Distribution in DC, from DC's 2006 Comprehensive Plan.

Land Use Distribution in DC, from DC’s 2006 Comprehensive Plan.

The graphic doesn’t specify if the street figure refers to street right of way, or just the carriageway portion of the street, but not the ‘parking area.‘ Seattle’s planning documents also showa similar pattern: 26% of land city-wide used for streets, but also a higher percentage of downtown land devoted to streets.

Seattle land use distribution by neighborhood. Image from Seattle's 2005 Comprehensive Plan.

Seattle land use distribution by neighborhood. Image from Seattle’s 2005 Comprehensive Plan.

The Seattle calculation looks at land devoted to right of way for streets, rather than just impervious surface.

Making better or different use of existing right of way is one thing; however, once that right of way is set, it is very difficult to change. Transportation networks awfully path dependent. Chris Bradford looks at Austin’s post-war planning and the abandonment of the street grid – path dependence in action:

Back then, “planning” chiefly meant “planning streets.” It’s a shame that planning lost that focus. The street grid that permeated Austin in 1940  is of course still with us, and forms the backbone for a number of quite livable neighborhoods.

So what happened? Developers building large, planned subdivisions (Allandale, Barton Hills) continued to add decent street networks after 1940. But the City itself appears to have gotten out of the grid-planning business not long after this map was made…

Collectively, these could and should have been platted into 40 or so city blocks. Instead, they remain two big blobs of land. The lack of connectivity funnels traffic onto South Lamar and Manchaca; impedes east-west mobility, dividing eastern and western neighborhoods; forces people to make circuitous trips to run even simple errands; and forecloses any sort of low-intensity, mixed-use development in the area. Then there’s the sheer loss of public space: South Austin should have a few more miles more of public, connected streets than it has today.

Once the street grid is set, it is very difficult to change.

Street spaces over 100 years

For a nice Saturday morning post, David over at Greater Greater Washington points to a great video from San Francisco, circa 1905.  The video is shot from a cable car traveling down Market Street, San Francisco’s great axial street.  The clock tower of the Ferry Building terminates the view, all while pedestrians, horses, cars, streetcars, and just about every other mode of transport share in the controlled chaos of a street where all modes share space.

Our streets weren’t always so compartmentalized, with segregated spaces for cars, pedestrians, bikes, and so on.  David gives a hat tip to the Ludwig von Mises Institute for the video, where the free-market libertarians posting the comments attribute the resulting order to the power of markets to organize themselves.

Several, however, note the limitations of such an example as a case for removing all traffic restrictions and separations – changes in technology, mass, speed, and so on – as well as the fact that managed and planned order can indeed be more efficient than this type of organic order.  Another notes that some of the chaos may not have been completely authentic:

I saw this video before, with a commentator talking alongside it. The car that crosses the tracks and is barely missed by the streetcar is actually part of the filming team, asked to do that to keep things interesting. If you pay attention, you see him cutting accross [sic] many times, actually crisscrossing in front of the streetcar.

Yet another commenter points to an almost exact re-creation of the same video from 2005, this time making use of travel along the F-Market streetcar line.

The arrangement of street space, obviously, has changed.  So has San Francisco’s urban fabric, now complete with skyscrapers.  The older video just predates the devastating 1906 earthquake and fire, a major factor in re-shaping San Francisco’s urban form.  The comparison between the two is stark, both for the things that have changed, as well as for the things that have not.

Back at GGW, commenter Lance throws a few barbs about overhead wires obstructing vistas.  It’s worth noting that DC’s current streetcar plan does not have any long stretches of track along the main vista avenues, such as Pennsylvania Ave.  Under the idea of a hybrid solution and careful routing, we might not even need wires to cross those main vistas, yet alone run along them. It’s also worth noting that San Francisco’s wires in the 2005 video are not just for streetcars, but also electric trolley buses – a few of them are seen in the video itself.  Since trolley buses do not run on steel rails, they require two wires to act as a ground.