They were unable to agree on whether to pull over onto the side of the road and wait for the animals to move or whether they should slowly drive towards them in the hope they would eventually shift.
Eventually, they were able to get past safely.
It is estimated that there are around 5,500 bison in Yellowstone National Park with the male bison weighing up to 900kg and females reaching 450kg.
The NPS also state that the animals can be aggressive with the ability to run up to 30 miles an hour.
Europe's best national parks
Europe's best national parks
See Switzerland's nature in all its glory at the oldest national park in the Alps. Ibexes, chamois, marmots, northern hares, lizards and countless birds roam free and can be observed from the 80 kilometres of hiking paths. The Swiss National Park covers an area of 170 square kilometres and there are nature trails and excursions for everyone to enjoy its beauty.
The breathtaking mountain range of Sierra Nevada National Park in Andalucia is a haven for hikers and horse riders in the summer and skiers and snowboarders in the winter. With outstanding scenery shaped by high mountains, forests and torrential rivers this national park is one of the most beautiful in Spain and the second highest mountain range in Europe after the Alps with 15 peaks standing over 3,000 metres high. There are several natural mineral springs and over 2,000 plant species in Sierra Nevada. Reptiles, birds and Spanish ibexes are just some of the wild creatures you may encounter.
The Cevennes National Park is located in the mountains of the south of France and lies across the Languedoc-Roussillon and Rhône-Alpes regions. The vast open space is a maze of hill slopes, deep valleys, winding rivers and forests. The north of the park has more harsh and rugged terrain than the south and is perfect for hiking or cycling. Be sure to explore the small villages of La-Garde-Guerin and Le Pont-de-Montvert, which are picturesque with typically French stone houses.
This ancient national park in Latvia has been attracting visitors since the 19th century to its beautiful valleys, forests and caves. The town of Sigulda is one of the main attractions of Gauja and has steep rocks and caves on the banks of its river. Around Gauja you'll also find lots of historical monuments including hill forts, stone castles, churches, watermills and windmills. For sightings of wild animals don't miss the Ligatne nature trails, plus there are lots of ways to get active, like skiing, bobsledding, bungee jumping and hiking.
Located in north-eastern Finland, Oulanka National Park is a unique landscape made up of pine forests and river valleys with sandy banks and rapids. It's a top hiking site and boasts a variety of animal and plant species. In late summer there's an abundance of bilberries, mushrooms and wild orchids and Oulanka is home to rare butterflies, more than 100 different bird species, bear, lynx and moose. Follow the 80 km Karhunkierros hiking trail, which is the most popular in Finland to see the national park at its best.
England's largest national park is arguably one of the most beautiful areas in the UK with lakes, mountains and woodland forming its impressive scenery. There are 16 lakes, over 150 high peaks, 50 dales and 400 towns and villages within the 885 square miles of countryside. The abundance of wildlife, ancient woodland and diverse landscape make the Lake District National Park a top place for all to explore and there are lots of outdoor activities available including mountaineering, kayaking, walking and cycling.
The Kamenice River Canyon, Pravcice Gate and the lookouts near the village of Jetrichovice are some of the most interesting points in the Bohemian Switzerland National Park. 97 per cent of the area is covered in forests and it's home to some rare animal species like the garden dormouse, peregrine falcon and black stork. The unique timbered houses in the villages of Bohemian Switzerland complement its natural beauty and the rest of the landscape consists of ledges, canyons, sandstone towers and rocks that rise over the forests and captivate visitors.
This stunning national park was set up in 1992 mainly to protect the Loricato and Bosnian Pines as it is the last area in the world where the Loricato grows. Pollino is located in the Italian regions of Calabria and Basilicata and is made up of tall peaks that reach up to 2,300 metres, rolling hills and valleys. Some of the animal species that have been spotted here include the golden eagle, Italian wolf, roe deer and black woodpeckers. Delicious wild spinach and San Giorgio mushrooms grow here too and some of the top things to do are climbing the slopes of the steep mountains, cycling and walking.
Famous for the Skradinski Buk, a large waterfall with an 800 metre-long cascade and a reach of almost 46 metres, the Krka National Park is an area of enchanting beauty. Discover the Roski Slap cascades, Lake Visovac and its island monastery that boasts unique Byzantine and Mediterranean architecture, the Medu Gredama gorge and dramatic caves. There’s a lot to see and do at Krka and it's even possible to swim in the lower lake and go on canoe and kayak tours.
This unique space in eastern Germany has more than 36,000 hectares of Elbe sandstone massif that was created over a period of 100 million years by the Elbe River. The strange rock formations are a must-see and around the park there are chalky sandstone cliffs, valleys, gorges and mountains to explore. Rare species like the eagle owl, otter and the fat dormouse can be seen here and rock climbing is one of the activities you can try to make your visit unforgettable. Be sure to take in the panoramic views of the River Elbe from the Bastei rocks and check out the scenery from the river by hiring a rowing boat.