Urban Design

Traffic is a critical factor within urban areas: it has an important relevance in good part of the activities and the services provided to its citizens, and it must be taken into account when making decisions. The problem is that usually a complete traffic analysis is far too expensive, it falls well over budget or it significantly increases the final costs of urban design.

Betterways has developed an extremely efficient methodology, based on Rapid Prototyping, to provide a first qualitative answer to any question concerning positioning: positioning traffic detectors, emergency services, charge points, parking, or any other type of urban element.

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Rapid Prototyping was initially developed addressing three questions related to traffic sensors: which technologies to use, how many sensors are necessary and where to place those traffic sensors? Betterways defined these questions as a set covering problem (SCP) and has designed a heuristic process to give an answer to both questions. This methodology provides reliable and quantifiable results well balanced against total costs. Its use has expanded to cover other issues of urban design related to the nature of traffic in urban areas. And the same benefits can be associated to the use of traffic analysis for decision-making concerning any other type of system related to urban design.

The regular way of doing concerning sensor deployment has subordinated the placement of sensors to the main and on most occasions unique objective: provide the required information to the traffic control systems in urban areas with traffic lights, or information on intensities and speeds and occupancy for highways. The emergence of new objectives, like information for the user on travel times, the convenience to provide information about alternative routes and, finally, the penetration of new technologies (license plate recognition, Bluetooth, GPS, ...) have shown that the design of the sensor layout has to be approached carefully as a function of the objectives aimed to and also to maximize the return from a limited number of sensors. This is also related to the fact that a restricted budget sets a limit for the number of sensors to install, so it is better to determine which is the best solution that can be obtained in such a case and, consequently, which objectives may be reached.

Considering an urban network, there are three main alternatives as a function of the operational characteristics of the technology:

  1. Location of the sensors within a section (typical alternative to place magnetic loops, magnetometers, radar and CCTV)
  2. Location in intersections (in case of technologies like Bluetooth sensors to detect a fraction of all vehicles driving through the intersection)
  3. Hybrid solutions for a mix of different technologies to measure the most relevant type of data at each point of interest.

The search for procedures to formalize the design of the sensor layout and permit a rational decision making based on efficiency criteria previously defined, started with Yang and Zhou (1998), and it has lead to a proposal of a set of basic rules in order to improve the trial and error regular praxis based on the intuition and experience of the decision maker with the highest familiarity with a particular city. These rules have been widely accepted and make up the initial criteria on which the models for decision making are designed. The four main rules are:

  • OD covering rule: To guarantee that a certain proportion of the total number of trips among each OD pair is observed.
  • Maximum Flow rule: For a particular OD pair the fraction of flow between that OD pair with respect to the total flow is the possible maximum.
  • Maximum Flow Interception rule: The chosen sections to be provided with sensors must intercept the possible maximum quantity of flow.
  • Rule for the independency of sections: DCSs have to be placed so that the traffic flow measurements on the selected sections are not linearly dependent.

This last rule is obviously violated by the strategy of sensor placement subordinated to the requirements of traffic control systems, under which detectors concentrate along main avenues and around main intersections, clearly lineally dependent.

Betterways, through its experience and tools:

  • Approaches the location of sensors in sections and intersections in a flexible way.
  • Incorporates additional conditions that represent explicit objectives from the side of the decision maker, including budget conditions limiting the number of sensors to be installed.
  • Takes into account:
    • The topological structure of the network being analyzed and its implications for the placement of the sensors, especially in case of technologies whose sensors can be placed in intersections
    • Restrictions that allow the reconstruction of partial paths between sensor pairs like, for instance, sets of Bluetooth sensors
  • Explicitly considers:
    • The structure of the most plausible paths between each OD pair in the transport network being analyzed
    • The estimation of the traffic flows for each path
  • Allows an analysis of the sensibility of the quality of the solutions obtained.

How to overcome the mentioned challenges and how to be able of providing solutions beforehand in a quick and economic way? Betterways has successfully developed its own methodology and the tool to apply it which has been denominated RAPID PROTOTYPING.

This method consists on:

  1. Taking advantage of the geographic information available from GIS to import and edit a model
    Urban Design 1 Urban Design 2
  2. Identifying both the plausible paths and their flows, together with an analysis of the quality of the results
    Urban Design 3 Urban Design 4
  3. Optimizing the detector layout and carrying out an analysis of the results based on the objectives of the sensorization
    Urban Design 5 Urban Design 6