Thursday, July 28, 2011

Map happy

Most readers know that I am a bit of a GIS wonk.  I now have my hands on a new set of data, and a new range of questions.  Capt. Julio Talero is the GIS analyst at Lincoln Fire & Rescue, but I can’t help by dabbling a little myself on the weekends.  I leave the heavy lifting to him, but I can play a little, too.

In preparation for a meeting last week, I prepared a few simple slides for my iPad. Capt. Talero provided me with a set of four-minute travel time polygons.  Using ESRI’s ArcGIS and Network Analyst extension, he created these polygons, which represent coverage areas from each fire station within four minutes of hypothetical travel time: hypothetical because the method uses the speed limit of each street segment to perform the calculation.  In the real world, you don’t get a running start, your acceleration is not exactly like a Cobra 429, and there are plenty of motorists who either can’t hear your siren over their music, or freeze up in the inside lane.
This first map shows the location of the stations, and the four-minute polygon surrounding. There is a lot of overlap, and these 14 polygons are opaque: they are layered over or under the adjacent station’s four minute area. 

Overlap is good if it’s located in the right place: the areas where you are most likely to have a high volume of calls for service. If you want to have a reasonable response time to every address in the City, you have to consider both proximity to the fire station, AND the likelihood that the resources at that station are already committed.  In a busy area, the resources are more likely to be occupied elsewhere, so the response is not coming from the closest station anyway.  Here’s another map depicting the overlap areas:
In this map, each of the 14 polygons is shaded pink and semi-transparent.  As four-minute travel time areas overlap, the visual effect is that the color becomes more and more opaque—a hotter shade of pink.


Steve said...

I happened by some kind of incident near the library at 27th and South late yesterday afternoon. I had one my dogs at the vet and heard a lot of sirens while I was waiting. When I left and got up to the intersection, there were already a couple LFR vehicles on scene, and police (I think), but I was still hearing sirens, and traffic didn't seem to be moving in any direction. Finally, a fire truck came from the north driving down the wrong side of 27th, apparently having crossed over due to all the traffic backed up from South Street.

My original point was that I understand how response times depend a great deal on the traffic situation at the time. However, it came to me that this particular problem might not have been so bad if we could get 27th street widened from South down to Highway 2. It seems to me, everyone in Lincoln wants that done except for the rich country clubbers that live along it. The less well-to-do folks along north 27th were left with front doors about 10 feet from the street, but the city didn't worry about them.

While we're at it, 48th from M to Normal is a nightmare any more and should also be widened. Maybe that would help reduce the congestion on south 40th, too.

Anonymous said...

Class envy is an ugly thing to see. The big money rarely lives in the CC area anyway, opting more for subs like the ridge and firethorn.

Steve said...

Big money is relative, the houses in the area of question aren't owned by people working two part-time jobs in a Seven Eleven. I don't envy them, I just don't see why government should treat them differently. Besides, how do you know I'm not one of those living on the ridge, or firethorn? :)

Anonymous said...

Because you had a picture of your house on your blog, Steve.

Anonymous said...

You forgot to figure in the 75 mph speed most LFR trucks travel down
residental streets. Please hurry I've sprained my ankle

Steve said...

Anon 5:35,

You crafty dog, you! :)

Steve said...

By the way, the only exterior shot of a house on my blogs was not my house. If you could tell where I live from any of the others, you're quite the detective.

Anonymous said...

Anonymous 5:38: If it was YOUR ankle that was sprained, I'm sure you'd be glad that LFR was getting there as fast as they could. Please don't criticize them for doing their job (and they're damn good at it, too).

Watchful said...


I like your opaque to hot pink map. What would be interesting to me is a similar map of the stations with breakdowns at 3, 4 and 5 minute response times.
Looking at the time map, it is easy to identify areas which are difficult to access due to some sort of barrier like the airport property and no roads running south from West O between 1st and SW 84th.

There are also some rural fire districts which butt against some areas of the city where otherwise, the city fire department would have a more rapid response. One example is just north NW 48th at W Holdrege.

A house fire on the east side would be dispatched to LF&R while one on the west would be dispatched to SW Rural Fire. LFR Station 11, next to the airport versus S Folsom and nearly Pioneers. Those boundaries are not delineated on the maps but do have a bearing on the displayed outcome.

5:38 - I would question highly your statement that fire appratus travel 75 miles an hour on residential streets. When sirens are wailing, it may SEEM they are traveling fast as they go by.

If you have ever driven a vehicle as wide as a semi(which is the same as a fire engine) on a residential street, you would know that it is difficult to do at 25 miles an hour the let alone 3 times faster than the speed limit. In some areas, the way some people park, it is difficult to do in a skinny car!!

Not that I would offer you chase a fire rig responding to a call, but the next time you see one a couple of blocks behind you in the mirror, you might slow down to the posted speed limit and if not stuck at a traffic signal yourself, see how long they take to catch you. They seldom travel much over the posted limit. Maybe 5 to 10 at most.... about the same as most of the drivers you see without any sirens on their car.

Police cars? Well, their rate of travel to a "hot call" is a completely different story. They can navigate, corner and stop better than a heavy medic unit or fire engine.

Both are supposed to use all due care and caution necessary to get where they are going, in the most expedient manner possible.

Anonymous said...

@Steve: I'd say the house in your Harley pic is somewhere in NE Lincoln. Not necessarily your house though.