Technical characteristics (specs) of parking sensors are not just “specs” that make engineers happy – these often directly translate into additional revenue earned or operational costs savings, thus should be considered as important KPI’s for a smart parking project.
The following are several key KPI’s that you can impact your project’s reliability, CAPEX and OPEX. Relative importance will vary depending on a particular project and revenue and cost model of the operator.
- Battery life
- Detection accuracy
- Detection time
- Communication range
- Overall Reliability
- Surface-mount vs. in-ground design
- Replacement design
If a parking solution operator pays for battery replacement – it is estimated to equal to about ½ hour work time (including travel to the location, night operation) plus battery costs itself, adding c. $30/sensor price for each battery replacement. So a sensor with 10 years battery life vs. 3-4 years will provide at least $60 costs savings.
But for a majority of the situations, battery replacement on site is not a practically viable option in terms of the risk for sensor’s integrity and IP protection and quality control processes required during such replacement. If sensor is sent to a shop, this means a need for special software enabling sensors IDs swap and/or manual ID entrance – all still implying additional costs to operations.
Even if the sensor suppliers pay for the battery replacement, a need for battery replacement still puts a material reliability risk on the sensor’s continued operation and IT system data integrity due to the factors above.
Detection accuracy, despite relatively low absolute difference among competitors, becomes quite important when considering overall number of parking events. For example, for a 1000-space parking project*, comparing 95% average to 99.7%, the c. 5% difference could result in up to 250 cars per day misidentified (for a sample project below*). Resulting into these many either false-positive alert that a car has overstayed it’s allowed time, or false-negative – not showing the spot as occupied and, e.g. not charging the car parked in the location.
Both of these scenarios would result into significant costs for false deployment of enforcement officers, dealing with end-user complaints, parking fees not collected, penalties/tickets not collected.
Sensors with only one detection mechanism (usually magnetometer) are much more prone to errors than multi-sensor sensors. Magnetometer-only sensors can have particularly low accuracy for Electric Vehicles that do not have a traditional massive metal engine.
* Project assumption: 1000 parking spots situation, on-street. Average of 5 parking events per day. Total number of parking sessions – 5000 per day.
Detection time is critical to ensure parking session duration accuracy for busy parking areas (especially on-street). Sensors with longer detection times (e.g. 30-40 sec vs 5 sec.) can miss the car change-over event when another car pulls in within 10-15 seconds from the previous car leaving. In such scenario, there is a risk that the parking event will be recognized as one, charging a wrong car for the parking event or generating a false overstay violation in the areas with the max stay restrictions.
Sensor-base station communication range is important to:
- Reduce number of base stations (impact on cost)
- Enable semi-autonomous solutions for no-power remote parking lots (no need for power, solar panels on the site – base station can be located in a building 1-2 mile away)
Solar panels solution – will add at least $300-400 to each base station (panels, batteries), cannot be installed on thin poles (wind load restrictions).
Can be measured as MTBF (mean time between failures), or % failures per year. Nwave sensors will provide 99% per year hardware reliability (and we are constantly improving it!)
Most operators prefer an “install and forget” solution. Low reliability results in the overall higher OPEX costs related to sensor maintenance.
Surface-mount vs. in-ground design
It is our strong view that for a majority of parking applications that are not subject to heavy snow plowing and heavy truck traffic, surface-mount design is superior because it:
- Significantly reduces install and de-install time and cost
- Maintains pavement surface integrity
One of the key benefits of in-ground sensors, is that, by their installation nature, are less exposed to external elements and vehicle abuse. However, their major disadvantage is that they require drilling of the pavement for their installation – resulting in significantly higher installation and future maintenance cost (e.g. for battery replacement) vs. surface-mount sensors. Additional concern for flush-mount sensors is road surface integrity in freeze-prone regions – water can get into the micro-crack between the sensor and the road surface and result into road surface fissuring due to repeated freeze-thaw cycles.
While at Nwave we offer both surface-mount and flush-mount modifications of our sensors, we believe that 90%+ ground sensor smart parking solutions would be better off with the surface-mount sensor – for the reasons outlined above. The modern surface-mount sensor design, at least the Nwave’s sensors, has been perfected to withstand the weather, vehicle and street-cleaning abuse – without the need to drill the pavement surface.
The only true concern remaining for the surface-mount sensors is snow-plowing with a metal snow plow. For a large portion of the world, snow-plowing is not applicable at all or a very rare occurrence. For those regions that have irregular or moderate snow-coverage, we have a special snow-plow-resistant modification of our sensor base, that can withstand some substantial snow-plow abuse – as demonstrated by this video. And for those heavy snow coverage areas with heavy street snow plowing (think Alaska) or for extremely heavy truck traffic areas – this is where we believe a flush-mount sensor installation is truly justified.
It is beneficial to have a quick “drop in” design for when sensors will need to be replaced for maintenance or battery replacement.
Physical removal of the complete sensor from the pavement requires more time and carries a higher risk of damaging the sensor.
Nwave Solution advantage
Nwave solution boasts world-leading specs in all of the categories critical for a feature-rich, reliable and cost-effective modern smart parking solution. Please refer to www.nwave.io for more details.