Some cities or communities develop an evacuation plan for use in case of an emergency. There are a variety of the explanation why metropolis officers may enact their plan, a major one being a pure catastrophe, comparable to a twister, flood, or wildfire. An evacuation plan might help the neighborhood extra successfully reply to an emergency, and so may assist save lives. Nevertheless, it may be troublesome for a metropolis to judge such a plan as a result of it isn’t sensible to have a complete city or metropolis rehearse a full blown evacuation. For instance, Mill Valley, a metropolis in northern California, created a wildfire evacuation plan however lacked an estimate for the way lengthy the evacuation would take.
At present we describe a case examine during which we teamed up with town of Mill Valley to check and enhance their evacuation plan. We define our method in our paper, “Mill Valley Evacuation Examine”. We began through the use of a visitors simulator to mannequin a citywide evacuation. The analysis objective was to offer town with detailed estimates for the way lengthy it could take to evacuate town, and, by learning the egress sample, to seek out modifications to make the plan simpler. Whereas our prior work on this topic supplied an estimate for the evacuation time and confirmed how the time might be diminished if sure highway modifications had been applied, it seems the suggestions in that paper — comparable to altering the variety of outgoing lanes on an arterial — weren’t possible. The present spherical of analysis improves upon the preliminary examine by extra precisely modeling the quantity and beginning places of automobiles, through the use of a extra lifelike map, and by working carefully with metropolis officers to make sure that advisable modifications to the plan are deemed viable.
Geography and methodology
Mill Valley is in Marin County, California, north of San Francisco. Most of the residences are positioned on the steep hillsides of a number of valleys surrounded by dense redwood forests.
Aerial views of Mill Valley, courtesy of the Metropolis of Mill Valley.
Lots of these residences are in areas which have just one exit course, towards the city heart. From there the very best evacuation route is towards Freeway 101, which is within the flat a part of town and is the probably space to be removed from potential wildfires. Some neighborhoods produce other routes that lead away from each town and Freeway 101, however these routes move by means of hilly forested areas, which might be harmful or impassable throughout a wildfire. So, the evacuation plan directs all automobiles west of Freeway 101 to go east, to the freeway (see map under). The neighborhoods east of Freeway 101 are usually not included within the simulation as a result of they’re away from areas with a excessive hearth hazard score, and are near the freeway.
Mill Valley has about 11,400 households west of Freeway 101. Most Mill Valley households have two automobiles. Evacuation instances scale with the variety of automobiles, so it’s within the widespread curiosity to reduce the variety of automobiles used throughout an evacuation. To that finish, Mill Valley has a public consciousness marketing campaign geared toward having every family evacuate in a single car. Whereas nobody is aware of what number of automobiles could be used throughout an evacuation, it’s secure to imagine it’s on common between one and two per family. The essential evacuation downside, then, is tips on how to effectively get between 11 and 23 thousand automobiles from the assorted residences onto one of many three units of Freeway 101 on-ramps.
The simulated a part of Mill Valley west of Freeway 101 is contained in the blue border. Freeway 101 is proven in inexperienced. The crimson squares point out the three units of Freeway 101 on-ramps. The pink space has the very best hearth hazard score.
The present work makes use of the identical basic methodology because the earlier analysis, specifically, working the open supply SUMO agent-based visitors simulator on a map of Mill Valley. The visitors simulator fashions visitors by simulating every car individually. The detailed behaviors of automobiles are dictated by a car-following mannequin. Every car is given a degree and time at which to begin and an preliminary route. The routes of most automobiles are up to date all through the simulation, relying on circumstances. To think about potential modifications in driver conduct below the excessive stress circumstances of an evacuation, the consequences of the “aggressiveness” of every automobile can also be investigated, however in our case the impacts are minimal. Some simplifying assumptions are that automobiles originate at residential addresses and the roads and highways are initially empty. These assumptions correspond roughly to circumstances that might be encountered if an evacuation occurs in the midst of the night time. The principle inputs within the simulation are the highway community, the family places, the common variety of automobiles per family, and a departure temporal distribution. Now we have to make assumptions in regards to the departure distribution. After discussing with town officers, we selected a distribution such that the majority automobiles depart inside an hour.
4 bottlenecks
Mill Valley has three units of Freeway 101 on-ramps: northern, center, and southern. All of the automobiles should use certainly one of these units of on-ramps to achieve their vacation spot (both the northernmost or southernmost phase of Freeway 101 included in our map). On condition that we’re solely involved with the vast majority of Mill Valley that lies west of the freeway, there are two lanes that method the northern on-ramps, and one lane that approaches every of the center and southern on-ramps. Since each car has to move over certainly one of these 4 lanes to achieve the freeway, they’re the bottlenecks. Given the geography and present infrastructure, including extra lanes is infeasible. The intention of this analysis, then, is to attempt to modify visitors patterns to maximise the speed of visitors on every of the 4 lanes.
Evacuation plan
After we began this analysis, Mill Valley had a preliminary evacuation plan. It included modifying visitors patterns — disabling visitors lights and altering visitors guidelines — on a couple of highway segments, in addition to specifying the assets (visitors officers, signage) essential to implement the modifications. For instance, a two-way highway could also be modified to a one-way highway to double the variety of outgoing lanes. Quickly altering the course of visitors is named contraflow.
The plot under exhibits the simulated fraction of automobiles which have departed or reached their locations versus time, for 1, 1.5, and a couple of automobiles per family (left to proper). The dashed line on the far left exhibits the fraction which have departed. The stable black strains present the preliminary evacuation plan outcomes and the dotted strains point out the traditional highway community (baseline) outcomes. The preliminary evacuation plan considerably accelerates the evacuation.
The cumulative fraction of automobiles vs. time in hours. The demand curve is proven within the dashed line on the far left. The stable strains present the preliminary evacuation plan curves for 1, 1.5 and a couple of automobiles per family (left to proper). The dotted strains present the identical for the baseline case.
We are able to perceive how efficient the preliminary evacuation plan is by measuring the charges on the bottlenecks. The under plots present the speed of visitors on every of the 4 lanes resulting in the freeway on-ramps for the case of 1.5 automobiles per family for each the baseline case (the traditional highway guidelines; proven shaded in grey) and the preliminary evacuation plan (proven outlined in black). The typical price per lane varies significantly within the totally different instances. It’s clear that, whereas the evacuation plan results in elevated evacuation charges, there’s room for enchancment. Particularly, the center on-ramps are fairly underutilized.
The charges of visitors on the 4 lanes resulting in Freeway 101 on-ramps for each the baseline case (regular highway guidelines; proven shaded in grey) and the preliminary evacuation plan (proven outlined in black).
Last evacuation plan
After learning the map and investigating totally different options, we, working along with metropolis officers, discovered a minimal set of recent highway modifications that considerably decrease the evacuation time in comparison with the preliminary evacuation plan (proven under). We name this the ultimate evacuation plan. It extends the contraflow part of the preliminary plan 1000 ft additional west, to a primary intersection. Crucially, this enables for one of many (usually) two outgoing lanes to be devoted to routing visitors to the center on-ramps. It additionally creates two outgoing lanes from that primary intersection clear by means of to the northern on-ramps, over ¾ of a mile to the east.
A map of the principle modifications within the closing evacuation plan. The crimson line exhibits that visitors heading north on Camino Alto will get diverted to the center Freeway 101 on-ramps. The blue line exhibits visitors within the northern lane of E Blithedale Ave will get routed on the brand new contraflow part.
The speed per lane plots evaluating the preliminary and closing evacuation plans are proven under for 1.5 automobiles per family. The simulation signifies that the ultimate plan will increase the common price of visitors on the lane resulting in the center on-ramps from about 4 automobiles per minute to about 18. It additionally will increase the by means of price of the northern on-ramps by over 60%.
The charges of visitors on the 4 lanes resulting in Freeway 101 on-ramps for each the preliminary case (proven shaded in grey) and the ultimate evacuation plan (proven outlined in black).
The under plot exhibits the cumulative fraction of automobiles vs. time, evaluating the instances of 1, 1.5 and a couple of automobiles per family for the preliminary and closing evacuation plans. The speedup is kind of vital, on the dimensions of hours. For instance, with 1.5 automobiles per family, it took 5.3 hours to evacuate town utilizing the preliminary evacuation plan, and solely 3.5 hours utilizing the ultimate plan.
The cumulative fraction of automobiles vs. time in hours. The demand curve is proven within the dashed line on the far left. The stable strains present the ultimate evacuation plan curves for 1, 1.5 and a couple of automobiles per family (left to proper). The dotted strains present the identical for the preliminary evacuation plan.
Conclusion
Evacuation plans might be essential in shortly getting many individuals to security in emergency conditions. Whereas some cities have visitors evacuation plans in place, it may be troublesome for officers to learn the way properly the plan works or whether or not it may be improved. Google Analysis helped Mill Valley take a look at and consider their evacuation plan by working visitors simulations. We discovered that, whereas the preliminary plan did velocity up the evacuation time, some minor modifications to the plan considerably expedited evacuation. We labored carefully with town throughout this analysis, and Mill Valley has adopted the ultimate plan. We had been in a position to present town with extra simulation particulars, together with outcomes for evacuating town one space at a time. Full particulars might be discovered within the paper.
Detailed suggestions for a selected evacuation plan are essentially particular to the realm below examine. So, the particular highway community modifications we discovered for Mill Valley are usually not immediately relevant for different cities. Nevertheless, we used solely public knowledge (highway community from OpenStreetMap; family data from census knowledge) and an open supply simulator (SUMO), so any metropolis or company may use the methodology utilized in our paper to acquire outcomes for his or her space.
Acknowledgements
We thank former Mayor John McCauley and Metropolis of Mill Valley personnel Tom Welch, Lindsay Haynes, Danielle Staude, Rick Navarro and Alan Piombo for quite a few discussions and suggestions, and Carla Bromberg for program administration.