2023 City Index for Mindful Travelers

In May 2022, KAYAK conducted an e-survey among 10,000 participants from the USA, Canada, Australia, Austria, Germany, Denmark, Spain, France, Sweden, and the UK via Cint’s panels. This survey revealed that around 83% of people say sustainability influences their summer 2022 travel plans - but around 55% feel there is a lack of travel options that they considered to be ‘sustainable’, and more than a third find it hard to make sustainable choices while on holiday. This shows that travelers seem to have sustainability top of mind when planning, but aren’t always able to fulfil their sustainability goals.

Subsequently, KAYAK conducted this data study in order to determine the options that a mindful traveler may have in a given city and show the traveler more sustainable actions they can take during their city trip. This project is based on a literature overview of sustainability, overtourism and related extensive data collection from a variety of sources. We’ve ranked 167 cities according to 28 factors that sustainability-focused travelers may take into account when making travel choices along the journey - from transportation options to the destination all the way to what activities the traveler can enjoy while there. Please, refer to the detailed factor descriptions below (‘Data sources & factor definitions’), as well as to the list of sources for theoretical background under ‘Literature’.

The factors were based on the three pillars of sustainability: environmental, socio-cultural and economic (Barbier, 1987). Similarly to Barbier, 1987, we also acknowledge the difficulty and discourse around operationalizing sustainability, while for purposes of usefulness and simplicity we have chosen this most widely referenced framework in the field. When applying the ideas to tourism we additionally rely on the UNWTO guidelines of sustainable development. Factors based on the environmental pillar are those that refer to greenhouse gas emissions reduction, air quality and consumption of water, land and energy. Socio-cultural based factors are those that deal with the local people, community and culture preservation. Economic-based factors are those that support the local economy and keep money local. Some factors may relate to more than one pillar.

The Travel Sustainable programme is a Booking Holdings programme designed for accommodation property owners that qualify for the programme by implementing practices that lower their environmental impact (like not using single-use plastics or investing in renewable energy) and that support local communities (such as putting money back into community projects and providing green spaces). We refer to such properties as ‘Travel Sustainable hotels’ in this index and methodology.

The most searched hotel city destinations worldwide have been identified based on searches conducted from 2021 Jan 01 - 2022 Mar 01 for the travel period 2022 Jan 01 - 2022 Dec 31. Then top cities per region and country were shortlisted to account for an even geographical representation. Finally, cities were further shortlisted based on data availability, which resulted in inclusion of a total of 167 cities in this analysis.

1. Weights: 24 out of the 28 factors have been assigned a weight indicating their importance (1 - lowest, 4 - highest). The factors dealing with share of Travel Sustainable hotels in a city, price difference between Travel Sustainable- and non-Travel Sustainable hotels, carbon accreditation of airports and levels of connectivity in ground transport (rail and ferries) are considered to be stronger indicators of options available for sustainability-focused travelers and were, therefore, assigned the highest weight (4). They are closely followed by factors related to local traffic as well as air quality and city attractiveness for longer stays. These high weights have been assigned to factors that seem to be most relevant regarding issues around overtourism (Peeters et al, 2018; Milano et al, 2019; Gossling et al, 2018; Oklevik et al, 2021). Lower weights have been assigned to factors in the Experience category, those related to infrastructure for getting around in the city as well as other factors that are not considered to be the main sustainability-related decision drivers of choosing a travel destination.

Seasonality indicator: The importance of flight price difference between peak and off-season has been weighted individually for each destination based on a seasonality level, which was calculated as a ratio between high and low search months.

Bonus points: Binary factors, including: Drinkable tap water, World Heritage Cities, Free walking tours and Commitment to Diversity & Inclusion were calculated as bonus points, i.e. a city would receive +1 extra point for any of these factors, with a maximum of 4 extra points. Similarly, for “Urban rail transit” a city would receive up to 3 extra points for having a high number of rail transport options.

2. Values within each factor were firstly normalised using formulas: score = 10 * (x - min(X)) / (max(X) - min(X)) and score = 10 - 10 * (x - min(X)) / (max(X) - min(X)) for inverted values (e.g. the amount of estimated car traffic in a city, where the lower percentage value is better).

3. The weighted average score of the factors has been calculated for each city.

4. Lastly, the weighted average score of the factors has been normalised using the formula score = 99 * ( ( (x - min(x) ) / ( (max(x) - min(x) ) ) + 1 to reach the final score on a scale between 1 and 100 (with 1 being the lowest and 100 the highest score).

The same procedure has been applied separately for scores within individual categories to determine category-level scores:

All sources have been accessed and data retrieved between 2022 Mar 01 – 2022 Sep 22. The numbers collected are based on the latest available data during the data collection period.

The ‘Traveling to’ category comprises four factors related to the choice of a destination and travel period (with possible mitigation of overtourism (Peeters et al., 2018; Milano et al., 2019)), as well as transportation mode (with possible reduction of associated carbon emissions):

Destination popularityShare of global hotel searches in a given city out of all hotel searches in the cities included in the analysis. Number of searches based on the search period June 2021 - August 2022 for travel period August 2021 - July 2022. Source: KAYAK internal data (retrieved on 2022 Sept 08)

Seasonal flight price differenceScaled percentage difference in flight prices between the highest and the lowest searched months across domestic, international and intercontinental flight routes. The bigger the price difference between peak and off-season flights, the better, as this encourages flying in off-season. Traveling during the off-season may have environmental and social benefits, including, but not limited to, not contributing to environmental pollution during high season, and reducing demand on infrastructure during high season. The importance of this price difference for the final score has been adjusted according to the destination’s seasonality, described in the ‘Scoring system’ section. Prices are based on searches conducted in the period June 2021 - August 2022 for travel period August 2021 - July 2022. Source: KAYAK internal data (retrieved on 2022 Sept 08)

Airport Carbon AccreditationA carbon management certification standard for airports. There are 6 levels of accreditation with 6 being the highest. Calculated is the average level across all airports and around in the city. Source: Airport Carbon Accreditation (retrieved on 2022 Sept 08) “Airport Carbon Accreditation is the only institutionally-endorsed, global carbon management certification programme for airports. It independently assesses and recognises the efforts of airports to manage and reduce their carbon emissions through 6 levels of certification: ‘Mapping’, ‘Reduction’, ‘Optimisation’, ‘Neutrality’, ‘Transformation’ and ‘Transition’.“

Trains and ferriesLevel of connectivity from 1-5 based on the train and ferry routes in a city, where level 1 indicates poor connectivity of city by train or ferry routes, and 5 denotes excellent connectivity. Calculated as absolute number of routes (tagged in OpenStreetMap) scaled by relative city size. Source: OpenStreetMap (retrieved on 2022 Sept 21). OpenStreetMap is a free, open geographic database updated and maintained by a community of volunteers.

The ‘Getting around’ category comprises nine factors related to local mobility trends and infrastructure:

Popularity of carsEstimated share of car use for work or school commute by the locals out of all transport modes. Source: Numbeo (Accessed on 15.09.2022). “Numbeo is a collection of Web pages containing numerical and other itemizable data about cities and countries, designed to enable anyone to contribute or modify content. Numbeo uses the wisdom of the crowd to obtain the most reliable information possible.”

EV charging stationsThe estimated number of EV charging stations for cars per mi2. Source: OpenChargeMap and OpenStreetMap (retrieved on 21.09.2022). “Open Charge Map is a non-commercial, non-profit, electric vehicle data service hosted and supported by a community of businesses, charities, developers and interested parties around the world.”

Price difference: Eco-friendly car rentalPercentage difference in eco-friendly (hybrid or electric) vs non-eco-friendly car rental price in a city. Prices based on the search period June 2021 - July 2022 for travel period August 2021 - July 2022 across all car types. Source: KAYAK internal data (retrieved on 06.09.2022)

Popularity of bikesEstimated share of bike use for work or school commute by the locals out of all transport modes. Source: Numbeo (Accessed on 15.09.2022)

Bike sharingThe estimated total number of shareable rental bikes across available operators in a city. Source: Bike-sharing World Map (retrieved on 06.09.2022). “A map of the world's bikeshare services (short-term bicycle rentals available at a network of unattended locations).”

Bike routesCalculated is the length (mi) of bike routes per mi2 in a city. Source: OpenStreetMap (retrieved on 21.09.2022)

Urban rail transitBonus point system on a scale 0 - 3 (low-high), indicating the level of alternative public transport infrastructure, based on the total number of tagged subway, tram, trolleybus, light rail, monorail, and funicular routes. 1 point was given for over 4, 2 points for over 10, and 3 for over 40 routes. Source: OpenStreetMap (retrieved on 21.09.2022)

Pedestrian-only roadsCalculated is the length (mi) of pedestrian-only roads per mi2 in a city. Source: OpenStreetMap (retrieved on 21.09.2022)

Wheelchair accessibilityThe number of tagged wheelchair-accessible places in a city, converted to a 4-level scale. The higher the level, the more wheelchair-accessible a given city is. Level 1 indicates less than 0.3 tagged wheelchair accessible places per square kilometre, level 2 denotes 0.3-1.3 per mi2, level 3 1.3-2.6 per mi2, and level 4 is more than 2.6 places per mi2. Source: OpenStreetMap (retrieved on 21.09.2022)

The ‘Stay’ category comprises six factors related to the length of stay, types of accommodations, and living conditions and habits:

Longer staysPresented is the average length of stay, which is treated as an indicator of how attractive a city is for longer stays. Longer stays may help promote social and economic sustainability because travelers have the time to go beyond the city centre (e.g. shop in local businesses on the outskirts), and help support more communities through tourism (Gössling et al, 2018; Oklevik et al, 2021). The average length of hotel stays (number of days) in a destination city, based on search period January 2021 - August 2022 for travel period September 2021 - September 2022. Source: KAYAK internal data (retrieved on 07.09.2022)

Hotel availabilityShare of Travel Sustainable hotels (Travel Sustainable Program, from Booking.com) out of all properties in a city. Source: KAYAK internal data (retrieved on 30.07.2022)

Hotel price differencePercentage difference in price between Travel Sustainable (Travel Sustainable Program, from Booking.com) - and non-Travel Sustainable hotels (Travel Sustainable Program, from Booking.com) in a city. Prices based on the search period June 2021 - July 2022 for travel period August 2021 - July 2022. Source: KAYAK internal data (retrieved on 08.09.2022)

Air qualityAverage Air Quality Index (AQI) for a city from the year 2021; scale 1-500 (best-worst). Source: Air Matters. “A global air-quality service provider: Providing real-time Air Quality Index & Allergy Pollen & Weather Data, as well as Protection Recommendations and Forecast.”

Recycling pointsThe number of tagged recycling points in a city, converted to a 5-level scale. The higher the level, the more recycling options there are in the city. Level 1 denotes less than 0.1 tagged recycling points or centres per mi2, level 2 indicates 0.1-0.5 per mi2, level 3: 0.5-1.3 per mi2, level 4: 1.3-2.6 per mi2, and level 5 more than 2.6 recycling points per mi2. Source: OpenStreetMap (retrieved on 21.09.2022)

Drinkable tap waterBinary variable indicating whether tap water is generally considered drinkable or not in a destination (country level).Source: CDC (accessed on 02.09.2022)

The ‘Experiences’ category comprises nine factors related to a range of things to do, accessibility & inclusion as well as cultural experiences for travelers:

Walking toursShare of city walking tours out of all sightseeing tours offered in a given city. Source: KAYAK internal data (retrieved on 09.08.2022)

Free walking toursBinary variable indicating whether free walking tours by locals are offered in a city and if they can be easily found on the internet. Source: Research based in August 2022

Wheelchair-accessible toursShare of wheelchair-accessible tours out of all tours offered in a city. Source: KAYAK internal data (retrieved on 09.08.2022)

Commitment to D&IBinary variable, indicating city’s commitment to Diversity & Inclusion by being a member of the International Coalition of Inclusive and Sustainable Cities (ICCAR) and/or having an undersigned declaration to combat hate, extremism and bigotry. Source: UNESCO ICCAR, The United States Conference of Mayors (as of 28.03.2022). “The International Coalition of Inclusive and Sustainable Cities - ICCAR was launched by UNESCO in 2004 to assist local authorities in combating discrimination in their capacity as policy maker and service provider in areas as diverse as education, employment, housing provision and cultural activities.”

Local marketsThe number of tagged marketplaces per mi2. Source: OpenStreetMap (retrieved on 21.09.2022)

Second-hand shopsThe number of tagged second-hand shops of all kinds in a city per mi2. Source: OpenStreetMap (retrieved on 21.09.2022)

World Heritage cityBinary variable, indicating whether a city is a member of the Organisation of World Heritage Cities. Source: Organization of World Heritage Cities (retrieved on 19.08.2022)

Museums and artThe number of tagged museums, galleries, art shops, and art centres in a city per mi2. Source: OpenStreetMap (retrieved on 21.09.2022)

TheatresThe number of tagged theatres in a city per mi2. Source: OpenStreetMap (retrieved on 21.09.2022)