We've done a lot of travel site design, for companies including EasyJet, Hotels.com, National Express East Coast. In honour of World Usability Day's transport theme this year, we've pulled together eight design and usability tips from our travel-related ethnographic research and usability testing.

1. Support multi-variable trade-offs

Some people prioritise the cost of the ticket whilst others prioritise the time of travel. The type of trip will cause a person to prioritise one of those variables over the other, but most booking journeys involve trading off these two factors. Successful travel booking interfaces help people understand how time and cost influence each other.

For a holiday maker, the choice of location, duration and hotel make the activity even more complex. "I can go to Rhodes from Manchester on the 16th for 300 pounds, and stay in the four star excelsior for 7 nights, or Cyprus from Gatwick on the 19th for 312 pounds and stay in the 5 star Grand for 6 nights." These are really complex decisions, made in conjunction with family or friends, so you'll need to pull out all the stops to design an interface that really helps.

2. Present a well-defined proposition

Trying to be all things to all people is very expensive. Players with a tightly-defined target market will always do better at serving their market than generalised players spread thin over lots of markets.

Know your market and offer a proposition that appeals to that market - whether it's group travel, business travel, family holidays, design hotels, skiing etc. Then build a site that profoundly and accurately addresses those people's behaviours and needs.

3. Fight "search fatigue"� - catch people early in the decision process

People are overwhelmed with choice in the travel market. On average, people in our research visited 22 sites before deciding to go with a provider which they visited 2.5 times. By making site that supports people early in the decision making process and helps them fast track the exploration and decision process, you create awareness in people's mind and they are more likely to go with you.

4. Surface the right information to help people make a decision

Choosing hotels is hard. People find it difficult and stressful to make decisions when their criteria are flexible and the field is large.

Good pictures, features, location with map, star rating, Trip Advisor rating, price per room/night (not per person), hotel name and short description are what matters most when sifting through lists of hotels. Enabling people to get this information without having to 'pogostick' is vital.

5. Focus on selling the experience not the product

Beyond the basic factors above, there's a whole list of things that users want to know before they make a decision. Focussing on the experience of staying in a hotel, rather than the generic factors, makes it easier for people to make that final choice.

For example, a hotel in Paris is not just a "3 star hotel in the city centre". It's a fantastic base in the vibrant Place de la Sorbonne, it's ideal for food lovers with 6 gourmet bistros, it captures the image of Paris with its view of the Eiffel Tower, it's ideal for families or ideal for romantic getaways. Understanding what a stay there will be like is what will help people to decide and to buy.

6. Be transparent and honest

Trust is a major sticking point for travel sites. In our research, users rarely trusted the price shown and were always prepared for some last minute surcharges.

Travel sites want to show low prices (excluding as many elements as possible), because they believe it help buyers get started. The flip side: a slippery and arduous booking process repels buyers (one where surcharges slowly build up, and cross-sells appear in your basket uninvited).

Would giving the real prices transparently build reputation and trust that exceed the pulling power of a low offer? No one knows for sure. We do know that removing some of the automatic cross-sells does produce a short term loss of revenue. But whether it offers a long term boost in loyalty, no one has yet had the guts to find out.

7. The seducible moment comes after the sale.

When people go into low-cost flight booking mode, they are very task-focussed and don't really care about anything else. We think that's a learned behaviour coming from the situation that a) the good flight deals go fast b) they need to concentrate to make sure they get rid of insurance etc.

Low cost flight booking is like bargain hunting, and trying to up-sell users during the booking process is like taking the bargain away from them. The seducible moment for up-sell is not really during the flight booking process, but after. Most travel sites are stuck in the business model of trying to up-sell during the booking process.

8. Ensure localisation is an actual part of the design phase.

The most planned and least actualised design stage is LOCALISATION. Lack of effective internationalisation and localisation is costing travel sites money.

There's a myth that Europe offers a unified culture with different languages, but it's not true. Language, rating systems, research, booking and payment behaviour vary significantly from country to country.

A simple example: some cultures will tend to assume that a rating of 1 is the best rating, others that a rating of 5 is the best. (The solution is to use a visual rating scale which is less ambiguous).

To maximise adoption, conversion and revenue, travel sites need to research, and test internationally. Using design skills from a range or different countries helps too.

A market opportunity: Design the next generation of travel sites.

People have very quickly learned how to dodge the failings of one website by jumping to another. In our research we have seen that people have no loyalty, there is no trust and that means that online travel companies will always have a major element of uncertainty in their future.

But the development of the web shows that people are open to new ideas and new ways of doing things. So we urge travel companies to innovate based on these design tips. Come up with the iPhone of the online travel industry. The opportunity is there for the taking.

Thanks to Louise, Peter, Karl, Lola, SimonJ, Ofer, Claire and Alejandra for the research and insights.