Futuristic solutions for present air quality struggles

“Today, you have walked 3 kilometres and used electric public transport for a total of 25 minutes. You saved 1.7kg of CO2. Your footprint is zero. Thank you for caring about Sofia’s air quality and for contributing to a greener future on Earth.”

This message could be a notification on Sofia citizens’ mobile phones as part of the INNOAIR project. In the Bulgarian capital, an app becomes the incentive for sustainable mobility patterns against poor air quality.

Sofiacoin: when sustainability gets recognised

A bonus gets unlocked per 50 kilometres of walking or 100 kilometres of riding in the city. The rewards avoid consumerism and boost sustainable mobility methods by offering free tickets for public transport, electric scooters or public bike service. Other recognitions involve entertainment plans such as free entry to Sofia Zoo.

Image credit: Daria Nepriakhina

For those that master sustainable mobility and score the maximum kilometres ridden by bike or walked, there are premium rewards every four months: technological devices such as tablets or even tickets for cultural events, like concerts.

Sevdalina Voynova, Director of Programmes at Sofia Development Association, explains the objective goes beyond rewarding citizens three times per year. “We show the historical data, which are the routes most travelled by bicycle or by pedestrians.” Those environmental organisations and citizens who came on board initially wanted more sustainable traffic promotion rewards or something experiential. “But more importantly, the biggest incentive for them was the more, the better. The more bicycles there are, the better the infrastructure conditions would be. And this is also a good decision-making tool for the city.” The busiest roads will be prioritised for maintenance or improvements.

Sofiacoin contributes with data, and other projects part of INNOAIR will benefit from it. For example, the pilot on on-demand public transport, which has never been tested before in the European Union.

Public transport on-demand

“We will drop fixed timetables and fixed routes except for the final stop, ” explains Sevdalina. The initiative will avoid empty journeys or inefficient (but pollutant) routes. “They will come and pick the passenger up from the nearest possible corner, which is no further than 250 – 300 metres away from where you called it.”

Image credit: Ant Rozetsky

The unprecedented service will start with five electric buses with two missions: serve new areas of the city that are less connected with the rest of Sofia, and try out the new efficient, sustainable mobility model.

“We will not have half-empty buses moving around just because it’s their timetable, and they must go there every 15 minutes or so.” The e-buses will move along a route map based on app submission. However, there will be a couple of pre-defined stops, so “if you’re an elderly person and you cannot use the app, then the easiest is just to wait there.”

180,000 people are expected to be directly engaging or indirectly influenced. But all 1.3 million people that live in the capital will undoubtedly benefit. Young families with children populate these areas of the Bulgarian capital; that’s why the city council expects this alternative to reduce the number of private cars used to go to work, school and other daily activities.

Sustainable algorithms

The council is working with partners and two Sofia public universities. For a service like this, a lot of data, analytics and algorithms are required.

Along with the most circulated roads and the number of people that moves in a greener way, much more data can be added to optimise the model: people per area, cars per family, the density of population, number of lines per road, peak traffic times, directions of the streets, and so on.

This is how you collect and create an ecosystem, a broad base for this innovation, and it’s everyone’s
— Sevdalina Voynova

All this data is put into algorithms to help develop an efficient on-demand transport service. But the platform itself is designed to keep learning on its own. “What I mean by self-learning is that when you order an on-demand minibus, and I order it, these algorithms will show the driver the optimal way to come and pick you up. It will hopefully pick people up at the optimal time, best routes, but also in terms of eco parameters. Because this also will show how to drive without congestion.” The truth is, even electric vehicles cause traffic jams for other participants on the road.

To avoid that, another solution has been developed. It also leverages machine learning to display “green corridors”. Green corridors can show the greenest, cleanest options to move from one part of town to the other. It could be using one type of transport or a combination of several. Also, other helpful information such as traffic density or road reparations will make citizens save CO2 particles and time.

INNOAIR activity during the European Mobility Week

An air quality challenge

CO2 rates are a problem in Sofia, where it is difficult to enjoy good air quality due to several factors. Some of them are historical: “The first reason is the structure of the economy that we inherited.” Also, high mountains surround the capital. This geographical position causes winter thermal inversions. When the fog starts and the air is moister, the polluted air stays on top of the city due to the absence of wind.

However, traffic has the highest impact on air quality. Bulgaria is one of the countries in Europe where the oldest cars can be found.

Image credit: Nabeel Syed

That’s why, in addition to the measures explained below, Sofia will implement a low emission zone, and they are also getting ready to introduce congestion charges. The Director points out these measures might be challenging and taken as restrictive. “As you can imagine, these are not very popular measures, so people are very divided. Some very much like them, but some very much don’t.”

Citizens might not be willing to accept the changes since it directly affects their daily lives and movement patterns. At the same time, however, people expect some change in mobility habits due to covid, Sevdalina adds.

“Some of the things we could change, others we cannot. But you work with what you can, and transport and traffic are important pollutants. We must change dramatically the way we move in the city and the transport services in the city.”

The project expects to save 172,100 tons of CO2 and 2,300 tons of nitrogen dioxide.

A constant green commitment

This project contributed to the candidacy of the European Green Capital 2023 that Sofia presented. Initiatives like these and the city’s firm commitment to the green transition resulted in them being awarded second place.

European Green Capital 2023 finalists

“On-demand transport -I really hope- is going to be a very successful experiment, and it’s going to be scaled up throughout the city and hopefully in other European cities as well.” In Sevdalina words, putting the client at the centre of the service is essential, and it is the future of public transport to a considerable extent. The council will present their candidacy for 2024.

“I’m glad that the bicycle associations and the pedestrian groups are onboard. And I’m glad that the universities are very much on board because they really see the practical application of what they study in real life, in the city. This is how you collect and create an ecosystem, a broad base for this innovation, and it’s everyone’s.”


INNOAIR project is co-financed by the European Regional Development Fund through the Urban Innovative Actions Initiative.

Main image credit: Eilis Garvey

Marta Buces Eurocities Writer
in numbers:
  • 180,000

    people are expected to be directly benefited from on-demand transportation
  • 172,100

    tons of CO2 will be spared
  • 2,300

    tons of nitrogen dioxide will be saved