Thursday, March 12, 2015

Desire lines

No, not the lines of people trying to pay for their shopping. Desire lines are lines drawn on a map that represent where people desire to go. When planning and designing infrastructure for active transport (especially pedestrians), desire lines are an essential indicator of how people will want to use the facility. This is because it may take extra effort to deviate off the route that gives you the shortest path to your destination. The less mechanical assistance you have, the more important the shortest path is to route choice.

It is important to realise that the shortest path is not necessarily the route that has the shortest distance. It tends to be the route that appears to be the most direct path to the destination from a point of decision. For the pedestrian this is usually the route that follows the 'line of sight' - a path that most closely matches a straight line route from where you stand to where you want to go.

When planning and designing active infrastructure you ignore desire lines at your peril. Here are two examples. 

The first is an old one that I see every day I ride to work. It is the link across Little Dock Street between the Kangaroo Point Bikeway and Vulture Street. This link is restricted as I bicycle-only connection. The planning intent was that pedestrians wanting to access Vulture Street would cross Little Dock Street at the Goodwill Bridge and use the bougainvillea pathway. Cyclists would use the Kangaroo Point Bikeway and exclusively use the link across Little Dock Street. sort of like the illustration below. The Kangaroo Point Bikeway and the pathway alongside it were designed with fences, kerbs and signs to ensure people stick to this arrangement.

All very nice and neat. However, this arrangement neglects to recognise that when walking people make their routing choices based primarily on desire lines in order to expend the least effort in reaching their destination. The infrastructure and regulation are only considered where they physically prevent a movement, or when the 'self-preservation' instinct overrides the 'least-effort' instinct.

The desire-lines for pedestrians between the Goodwill Bridge and Vulture Street can be shown as below. In addition to this major desire line there is also a minor pedestrian desire line between Vulture Street and the pathway going east along Little Dock Street.
The resulting pedestrian movements result in significant conflict between pedestrians and cyclists along a very narrow section of separated pathway (only 2m wide cycleway).
For the most part pedestrians recognise that they are crossing the bikeway and they are careful to not get in the way. They check before they cross and keep their eye out to avoid conflict, as can be seen in the picture below. Note the pedestrian in the background is also keeping an eye out to avoid conflicts on the narrow path.
In fact it is such a well-worn route that you can see the path through the vegetation that pedestrians take to avoid being in the way of cyclists.

But often this does not happen and conflict erupts. I almost witnessed a fist fight recently where a rather muscular pedestrian who had been walking in the middle of the bikeway shoved a cyclist when he tried to get past after ringing his bell. Usually this sort of conflict just results in some rude words being exchanged as the cyclist and pedestrian exchange their feelings of mutual dislike for each other. That time (and I am sure there have been many others) it could have ended tragically.

The solution to this is relatively simple, but will cost some money. What is needed is to provide sufficient space for both pedestrians and cyclists to make the link between the Kangaroo Point Bikeway and Vulture Street. More fences and signs will not solve the problem, it will just make it more frustrating for all users.

The next example is a more recent one - the landing of the Kurilpa Bridge on Tank Street. When designing this landing the engineers had great difficulty fitting in all the pedestrian, cyclist and vehicle movements. The complicating factor was the driveway off Tank Street for access to a parking garage. This wide driveway was adjacent to where the bridge landed and spills its load of pedestrians and cyclists. The designers came to the conclusion that the driveway entry and exit meant it was not possible to provide sufficient space to store pedestrians wanting to cross Tank Street. The large number of vehicles using Tank Street to access parking garages would have been too severely delayed by creating a shared zone for pedestrians and vehicles.

So the solution delivered was to prevent pedestrians and cyclists from crossing Tank Street where the bridge landed. A wall was constructed to prevent this movement and gardens planted to make it clear that pedestrians should not cross here. Fortunately as a compromise a speed hump was included on Tank Street to slow drivers down as they approached the parking lot driveway.

Unfortunately the pesky pedestrians had not studied engineering and they refused to comply.
 They just didn't seem to realise that this was not an approved maneuver.

 Within no time they had worn a path through the landscaping that was intended to prevent them from crossing.

Unfortunately the designers ignored the very obvious desire lines. The approved place to cross Tank Street was determined to be at North Quay and George Street (as below). That would ensure that any conflicts that would occur could be controlled.
What this design ignored was the very strong pedestrian desire lines between the coffee shops (and parking garage) on the north of Tank Street, and the offices and bridge on the south. It also ignored the fact that the proposed path between North Quay and the Kurilpa Bridge or south Tank Street was not at all obvious and was not on the pedestrian (and cyclist) desire line.
 So of course this resulted in pedestrians (and some cyclists) making 'unsafe' maneuvers.
 Thankfully a solution was retrofitted that better provides for pedestrian and cyclist desire lines.

It is unfortunate that desire lines were ignored in the initial design, as I am sure that a more elegant solution could have been found to this problem.

No comments: