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Measuring sidewalk accessibility

Comparison of geospatial imagery, LiDAR, and manual measurement for ADA self evaluations

As part of the Chicago Metropolitan Agency for Planning’s (CMAP) technical assistance program, CMAP has partnered with several communities across northeastern Illinois to create accessible community plans. These plans, once implemented, will help people of all abilities get around their communities safely and conveniently.

The accessibility plans also help communities comply with the Americans with Disabilities Act (ADA), which requires that all local governments conduct a self-evaluation of their sidewalks, crosswalks, streets, and parking (“public right-of-way”), creating an inventory of accessibility barriers. Governments with 50 or more employees muse also create a transition plan to mitigate or remove the barriers identified in their self-evaluation.

CMAP had access to various data collection tools to create accessible community plans with our municipal partners. This article provides an overview of the features, cost, and accuracy of the primary survey tools: LiDAR, Ecopia (geospatial imagery), Project Sidewalk (geospatial imagery), and manual data collection. These tools may be used individually or in tandem to complete a self-evaluation.

Note: CMAP partnered with the Illinois Department of Transportation to purchase Ecopia, a tool that uses geospatial imagery as a survey method. This partnership allows for free use of Ecopia to communities in northeastern Illinois.

Collection tools overview

• LiDAR: LiDAR is a laser imaging, detection, and ranging technology that uses light to determine the location of objects. Surveyors collect raw data on smartphones or sensor arrays attached to vehicles. The raw data is converted from 4D images into CAD and GIS datasets, tagged using machine learning technologies and audited by computer technicians. Surveyors then manually check traffic signals, crosswalks, vertical displacements and on-street parking for accessibility. Communities can rent mobile LiDAR devices and perform the survey themselves or outsource to a LiDAR firm.
• Ecopia: In 2023 CMAP procured Ecopia.ai’s Advanced Transportation Right-of-Way tool which uses a combination of raw images, machine learning, human annotation, and vector-based information to create an ArcGIS Shapefile and data tables summarizing features identified. Ecopia is available for local governments in northeastern Illinois region at no cost.
• Project Sidewalk: Project Sidewalk is a free online tool that relies on crowdsourced data to share information on sidewalk accessibility. It uses Google Street View imagery to label sidewalk infrastructure and identify accessibility barriers.
• Manual collection: Manual data collection requires trained engineers and technicians to survey the sidewalks, crosswalks, and streets for ADA compliance. Surveyors should be knowledgeable about accessibility compliance, completing field surveys, and taking measurements.

Method comparison

LiDAR, Ecopia, Project Sidewalk, and manual data collection each capture a different range of features — with varying accuracy and costs — of the elements defined by the Public Right-of-Way Accessibility Guidelines (PROWAG). Some key takeaways from CMAP’s field experiences include:

• LiDAR technology provides the greatest depth, breadth, and consistency of information on the accessibility of the public right-of-way — but at a considerable cost.
• Ecopia covers the fewest number of public right-of-way features listed in PROWAG and is the least accurate of the methods compared, but it is free to local governments in the CMAP region.
• Project Sidewalk can capture the presence of sidewalk, curb ramps, and barriers such as panel heaves, but does not have the ability to measure widths, running slopes, or cross slopes.
• With sufficient training, manual data collection can capture major features of the public right-of-way but tended to be less accurate and consistent than LiDAR. The cost is moderate.

The table below compares the major features of each data collection approach. Please note that the total number of features is not compared against the number of features used to measure compliance with PROWAG, rather is an overview of all features the tool is able to measure.

Feature comparison

In general, LiDAR provides the most accurate, precise and comprehensive analysis of the public right-of-way. In addition to highly accurate measurements, the software can calculate cost of repair for individual sidewalk panels, curbs ramps and intersections. LiDAR has limitations: it cannot identify accessible parking spaces, signalized intersections, or vertical displacements in the sidewalk. Also, given the complexity of the machine learning process, it is difficult to reverse-engineer mistakes.

Ecopia is best used for rough estimates of the length of the public right-of-way and counts of intersections. Users should be aware that the tool tends to overestimates the width of sidewalks; sidewalk width is a component of accessibility compliance, so Ecopia is not a recommended tool for this element.

Project Sidewalk is useful for identifying accessibility barriers in the public right-of-way, such as the presence of sidewalks and ramps and vertical displacements in sidewalks. This allows for high-level understanding and prioritization of the pedestrian network; however, manual measurements are still required to measure the level of compliance for most Title II features.

Manual collection is best suited for local governments with well-trained field surveyors capable of taking accurate measurements. Manual data collection can analyze accessible parking spaces and is currently the only way to measure vertical displacements in sidewalks.

The table below illustrates which features are captured by each data collection tool. Only manual measurements capture all the features. Municipalities typically use a mix of tools to support a robust survey of sidewalks, crosswalks, streets, and parking.

Cost comparison

The price of CMAP’s accessible communities plans varied widely by municipality, even when controlling for miles of sidewalk, contractor, and data collection method. The table below details the cost of self-evaluations for each municipality as of April 2025. Compared to Table 1, the pricing below incorporates staff hours required to use the tool. LiDAR was the most expensive data collection method. This is generally due to the use of a third-party contractor to both collect and analyze the data. LiDAR may also require additional manual spot checks to ensure proper calibration for feature measurement. Manual data collection was cheaper.

It is important to note that data collection represents only one component of the self-evaluation and transition plan process, and therefore accounts for just a portion of the total cost of developing these plans. Between 2022 and 2025, CMAP contracted with three consulting firms to complete a total of 16 ADA public right-of-way transition plans. The average plan cost was $240,000, with individual contracts ranging from $120,000 to $449,000. While communities with fewer linear miles of sidewalk or curb ramps generally incurred lower costs, additional factors such as the availability of existing data, the depth of analysis and prioritization, the level of public engagement, and the chosen data collection methodology also influenced total project cost.

The average total cost per mile of manual data collection across all 3 municipalities is $1,600. The portion of manual projects that were evaluated using Project Sidewalk was $64 dollars per mile, a 96 percent savings over deploying surveyors in the field. While Project Sidewalk is free, this cost includes manual labor. Project Sidewalk has a similar level of accuracy as Ecopia.

Accuracy

Ecopia data can be a starting point to understand where the sidewalk is very narrow or has major gaps but is the least accurate of the self-evaluation methods analyzed by CMAP. Ecopia uses aerial photography resulting in an inability to analyze slopes, grades, vertical displacements, signalized intersections or parking spots. A review of using Ecopia data to evaluate public right-of-way compliance found that Ecopia provides imprecise measurements on sidewalk widths and rough counts of street crossing features. Additionally, trees, tall buildings and cloud cover can prevent clear photographs, further degrading the quality of analysis. This tool provides a single snapshot in time (CMAP used 2023 Ecopia data); therefore, recent changes to the public right-of-way are not reflected.

LiDAR is the most accurate tool to evaluate the public right-of-way. LiDAR outperforms other tools using a smart level for slope and cross-slope measurements, captures 372 public right-of-way features and automatically computes scores for quality of public right-of-way. LiDAR also ensures consistency across the surveyed territory which can be inconsistent in manual measurement. LiDAR data is more up to date than geospatial imagery, which sometimes has images that are years old. However, as noted previously, manual spot checks should be used to ensure the equipment is properly calibrated to accurately capture data.

Project Sidewalk uses digital photography and manual inputs to collect data; however, incorrect inputs by the user and/or outdated digital photography may impact accuracy. A 2024 study on the use of Project Sidewalk found for one project that used “12,191 labels across 35.9 miles of streets, with a total of 19,396 validations [had] an accuracy rate (calculated by user validation of labels) of 93.1%.” Project Sidewalk also requires some training to ensure consistency of labels among data collectors.

The accuracy and precision of manual data collection is dependent on the quality of training and tools used. Manual measurements introduce human error, therefore experience using complex field measurement tools and accessibility guidelines is important for consistency across surveyors, along with a robust QA/QC of collected data. Depending on the data collection tools used, aggregating data from different surveyors and averaging scores can be logistically difficult and time intensive. With sufficient training and record keeping, manual data collection can provide high quality assessments of the public right-of-way.

Supplemental data gathering tools

CMAP provides data for municipal and public use. Data for municipal use is available from Navteq, HERE, and Ecopia. The CMAP Regional Sidewalk Inventory is available to understand the characteristics of sidewalks. Municipalities and nonprofits can partner with Project Sidewalk to record and digest data about the sidewalk network are available online. Below are a short description of each dataset and its relevant features.

• Navteq: Navteq is a digital mapping company that provides automotive grade maps. They are the trusted source for data on streets, roads and highways and the data was most recently updated in 2023. Data are available to municipalities in aggregate results (e.g., miles of centerline per town) as excel files.
• HERE data: HERE is a digital mapping platform with access to over 310 million miles of probe and sensor data. The tool provides high quality maps with accuracy to the centimeter. HERE data was last updated in 2022 and is most helpful for measuring length in miles of street centerlines. Data are available to municipalities in aggregate results (e.g., miles of centerline per town) as excel files.
• Regional Sidewalk Inventory: Produced by CMAP in 2018, the Regional Sidewalk Inventory analyzes 30,000 miles of roads in Cook, DuPage, Kane, Lake, McHenry, and Will counties to determine the existence of sidewalks on one or both sides of the street and whether there is a barrier between traffic and the sidewalk. The dataset includes miles of off-street paths and a sidewalk gap analysis.

For more information regarding these data sets, please contact Michael Collins at mcollins@cmap.illinois.gov.